JUST BEFORE SUNRISE, Captain Iván Castro feels his way across his hotel room to the bathroom sink. He stands before the mirror, his left eye wandering up and to the left, his right eyelid shut flat against an empty socket. He touches his right ear, then his sideburn. He shaves it, dry, a couple strokes down, a couple up. Repeats on the opposite side. Today, in particular, he wants to look good.

After the 44-year-old combs his salt-and-pepper hair, parted on the left, he sits down on his bed and dresses, the April morning light gleaming now off his stainless silver bracelet, the one bearing the names of Ralph Porras and Justin Dreese. He pulls on a dri-fit T-shirt with a U.S. Army Special Forces insignia. Above it is his name and the phrase "Blind Runner." Below it is another phrase: "I WILL NEVER QUIT."

And he won't, even though his knees and his back and his right hip ache, even though the marathon he'll run today, the most famous one, in Boston, will be his 14th in the past 15 months. Honestly, he thought about not making the trip from his home in Fort Bragg, N.C., but between backing out or running another marathon, backing out sounded worse. He gets asked a lot, Why do you keep doing this? Pushing yourself? Alienating some of those closest to you? The simplest answer: Backing out has always sounded worse.

And so Castro downs an Extra Strength Tylenol and waits. A few minutes later, he hears a knock at the door. Lt. Col. Michael P. Sullivan enters, wearing a matching shirt, only with the word "Guide" on the back.

"Hey there, sexiness," Castro says, grinning, his voice light and playful. "Lookin' good today."

Sullivan laughs.

"How'd you sleep?" Castro asks.

"Good, good. You?"

"Man, that 5 a.m. s--- comes too early."

Castro pulls on black sunglasses, then grabs his pack and his white-and-red-striped cane. An hour later, he's riding in one of 16 buses filled with military and police, headed for the starting line and one of the toughest days of his life.

SIX YEARS AGO, Castro deployed to Iraq as a first lieutenant, leading a platoon for the 82nd Airborne Division. Toward the end of August 2006, he volunteered for an offensive operations mission to secure Yusufiyah, a small town about 25 miles southwest of Baghdad. He led three teams of snipers -- about 15 men total -- to provide overwatch security at a compound his battalion had occupied.

The afternoon of Sept. 1, the Americans came under heavy mortar fire while battling Iraqi insurgents from the roof of a one-story building within the compound. A guy named Mercado got ripped in half up there. As night fell and the fighting stopped, Castro was ordered to take four men -- a radio operator and three snipers -- and replace Mercado's team. On the lookout for potential threats, the soldiers crawled on the flat roof, and Castro took to the front beside Pfc. Justin Dreese and Staff Sgt. Ralph Porras. A muddy brick wall stood before them, and beyond that a dirt road, shrubs and other buildings as squalid-looking as the one they stood on. Everything was beige.

Castro let his men sleep in shifts. He knew the insurgents would only engage during the day, when they could better blend in with the civilians in the streets, houses and shops below. "They won't attack at night," Castro said. "We own the night." When he could, he catnapped. In one dream he and his wife, Evelyn, lounged on the beach, margaritas in hand and the ocean at their toes.

Soon after sunrise, Castro sought safer ground. "Gonna be hot today," he said. He and Dreese and Porras stood near the spot where Mercado had died the day before, and Castro worried the mortars would soon find them again. He wanted to find a more secure spot within the compound where he could still battle insurgents.

He saw a ledge of a building under construction a football field away, at 4 o'clock. That's the spot, he thought. Castro picked up a radio to request permission to leave the roof, mashed the transmit button

A scream split the air, and then the earth exploded behind the building. The roof shook.

"Where'd that hit?" someone barked through the radio. "Where the f--- did that hit?"

Castro ignored him, screamed at Porras and Dreese. "Get off the roof! Get off the f------ roof!"

He never heard the second mortar land.

CASTRO HAS RUN Boston three times already. He'd like a time under four hours today -- a Boston best -- but at mid-morning, as he and Sullivan ride to the start of the race in Hopkinton, it's already 65 degrees. The high is supposed to reach the mid-80s.

"It's gonna be hot today," Castro says.

Sullivan agrees. "It's going to be interesting with that heat."

"Yeah man, I might run it naked," Castro says. "I could be a stripper, you know."

Sullivan laughs, and a few others on the bus laugh with him.

"Yeah, OK," Sullivan says. "My new goal for the day just became to keep your clothes on."

The exchange eases Sullivan's nerves. Sullivan is not Castro's normal guide. That'd be Lt. Col. Fred Dummar, laid up in Fort Bragg, having blown out his ACL during an airborn operation drill about six weeks ago. After Dummar got hurt, he recruited Sullivan to help Castro. Sullivan didn't hesitate. He's run ultra-100s and admires Castro greatly. But he and Castro have only been able to train three times in the past month -- one 4-mile run and two 6-milers. Not exactly ideal training to run the Boston Marathon in four hours.

On top of that, there's the pain. Castro's left knee needed reconstructive ACL surgery in 2001. His sciatic nerve still hurts from the mortar. And all the running has turned his right hip arthritic -- it grinds bone-on-bone. Add in the heat and Castro tells himself he'll be happy with a time under five hours.

After they unload in Hopkinton, Castro and Sullivan join about 50 other military personnel in a corner of the parking lot for Mass. A Catholic priest presides, wearing running shorts, a sleeveless T-shirt and lots of sunscreen. TV helicopters whop loudly above, and the priest yells at his congregants.

"You've all been through hell so this is nothing!" he says. "Only one percent of the world ever finishes a marathon, and you're the one percent of those, you lucky bastards, to run this one, the Super Bowl of Marathons. God will protect you. Run in His grace. Pain and fatigue and even this heat are all only so much bulls--- ! Let us pray! Our Father "

After communion, Castro, who's already sweating, says to Sullivan, "Holy s---, it's really f------ hot out here. People are gonna drop out left and right." He grins. "But you don't worry about it. You fall out, I'll carry you. Bones." He extends his fist; Sullivan bumps it.

Castro takes another Tylenol before they head to the starting line. Castro holds a shoelace looped around his left hand; Sullivan holds the other end in his right.

A pair of spectators see them, and one says, "Oh, man, cool, they're tethered together -- they're like, never going to leave each other." Then Castro and Sullivan walk past, and the spectators see their shirts. They gawk, whisper sideways, "Holy f---, dude," one says. "You see that?"

"Yeah," the other says. "That dude is f------ blind!"

Women come up to them crying so hard they can't speak, pointing at the shirts. Soldiers hoo-rah and salute. If they react like that to a shirt, Castro thinks, maybe he should run naked. Show everyone his scars, gashing up his arms, his shoulders, across his back, with shrapnel dotting his flesh. Under his shorts and up and down his legs, it's more of the same. It's what it looks like when a body that should've died in a warzone didn't.

NOBODY KNEW who he was until they checked the dog tags. It seemed like the whole right half of Castro's face was gone. A bone stuck out of his left arm. Where parts of his body would have been -- his shoulder, his buttocks, parts of his legs, his right index finger -- there were gaping, bloody holes. When medics secured him into the chopper, Castro, incoherent but somehow alive, struggled so much that they had to strap him down and pump him with sedatives.

Three days later he was at Walter Reed National Military Medical Center in Bethesda, Md., just outside Washington, where many wounded soldiers from Iraq and Afghanistan recuperate, and where doctors said Castro would die within a week. When his wife Evelyn walked into his room and saw his bloated body, missing half a face and pounds of flesh, she cried out to God, then collapsed.

They had met seven years earlier at the Coral Hamaca resort in the Dominican Republic. She'd flown down with her mom and aunt from New York, where she was finishing her bachelor's degree in psychology. He'd come alone, from Fort Bragg. He watched her for three days before he finally approached her at the resort club one night. The DJ was playing merengue. Ivan asked Evelyn to dance. She said no. He dramatically feigned anguish and said he was heading to the bar to drown his misery. She laughed hard. When the next song started -- something by Elvis Crespo -- she asked him to dance.

They spent the whole night together. She was gorgeous and fiery and smart, and he made her laugh and laugh. She asked him what he did, and for more than an hour he talked about the Army. He grew up in Puerto Rico and had brothers and cousins and uncles in the military, and he'd joined the Junior ROTC in high school. He attended college for four years but was still shy of a degree, and in 1990 moved to the States where he could be a real soldier full-time. He loved the sense of purpose, he explained to Evelyn. He loved the adrenaline rush the military gave him, unlike anything else.

Castro was promoted three times in four years. He went on missions to more than a dozen countries. He told her how he earned a spot in Ranger School in 1992, fighting for one of the two available positions through two days of intense, insane workouts. Day 1 was nonstop, Castro said, filled with every military exercise you can imagine. The next morning, the few left standing -- a dozen, maybe -- were told to shoulder their 65-pound rucksacks and march until they dropped. Castro marched until they gave him his spot, nearly 24 hours later.

"How?" Evelyn asked him.

"Being a soldier, you just do all you can as long as you still can," he said.

He told her about the battles he'd fought in, in the Gulf War and the Balkans, and about the Columbian military forces he'd trained in South America. He had earned countless badges, tabs, honors. When he led, his men loved it. Evelyn later joked with Ivan that it was like he was a cell phone stuck on "send" that night. On and on about the Army.

Evelyn asked him why he'd come to the Dominican alone. He said his mom had just died back home in Puerto Rico.

"What?" she replied. "Should you be here if your mom just died?"

"Well, my mom never likes to see me sad."

When they left the Dominican, Castro returned to Fort Bragg and Evelyn to New York. For a year their love bloomed, and they made the distance work. He would become a Green Beret in 2000, ultimately joining Special Forces Operational Detachment Alpha 781 -- an A-Team. In December that year, without telling her, he brought a U-Haul to New York. While she finished her last class, he packed up her stuff, and when she walked out of the building, he was there waiting with the truck. She didn't even walk the stage to get her diploma. On New Year's Day 2001, she moved with him to North Carolina. In June that year, they married.

Five years later, at the hospital in Bethesda, Evelyn fought for Castro like the best of soldiers. She refused the doctors who wanted her to sign donor release forms should Castro die in one of his nearly dozen emergency surgeries. "That's not an option you're allowed to have while you work on him," she told them. She dragged priests and Fransiscan monks into his room. She hung pictures of him everywhere -- for the doctors, she said, to show them they fought for a real person, not an exploded, comatose mess.

Two months after doctors said he'd die, Castro woke up. He'd lost virtually all ability to move. The first thing he asked Evelyn was for something to spit in, and then, "Porras and Dreese?"

"They died, baby." He wished he hadn't woken up: A good lieutenant keeps his guys safe.

In the days to come he asked for more and more morphine. The drug deadened his pain, but it couldn't stop the phantom visions. One day, Evelyn walked in, and he said he saw her, his surviving eye's sight restored. He shouted, and she ran to his side, crying, both of them ecstatic. But then his eye didn't follow her from the door.

"Are you sure?" she said. "Are you sure you see me?"

"Yes!" His eye darted in her direction. He saw her form-fitting black long-sleeved T-shirt and white capris. He saw the brown hair falling over her shoulders. "You are so beautiful." But instead of hair his hand hit air, and Evelyn told him she wore jeans and a pink tank top.

"Just turn on the lights," he'd say.

"Baby, the lights are already on."

When the doctors told him the blindness was irreversible, he felt a rage and despair that made him feel like his head would explode.

Castro began therapy a week after waking up, and he only halfheartedly endured the rehab sessions with a 6-foot-tall girl he called "Katie the Physical Terrorist." The first time she asked him to stand, he couldn't. He could barely lift a one-pound dumbbell.

Evelyn tried to focus him on the positives. Obliterated as his body was, his brain was OK -- remarkable considering that traumatic brain injury, or TBI, has become the trademark of the Iraq and Afghanistan wars, and that thousands of soldiers sent to Walter Reed had to battle it. But in a way Castro wished he'd not been spared, because an intact brain meant the other thing he could actually see was exactly how much his life had been ruined. He'd ask, "What kind of man can I even be?"

IT'S SO HOT in Boston today that race officials allow runners to defer a year. About 2,000 who registered don't start. Another 2,000 will need medical attention. Medical tents will overflow with passed-out runners on cots outside. More than 150 will be taken by ambulance to hospitals. And by Mile 6, Castro's legs burn like he's run 20. Four miles later, the lack of training and the heat leave Castro wobbling, and he's gone from wanting to finish in under five hours to just wanting to finish.

He's quit just one marathon in his life. It was about a year ago. Some idiot cut him off and stopped dead for water, and Castro crashed into him. Just brutalized that arthritic hip. He dropped out halfway through and regretted it immediately. The hip hurt, but quitting killed.

At Mile 10, he says to Sullivan, quietly, "If I'm going to finish this, we gotta play it smart."

WHEN EVELYN walked the halls with Castro, as part of his rehab, she noticed other soldiers, stricken with TBI, sitting beside their wives and kids, fully awake but hopelessly unaware.

"I'm so glad you still know me," she said. Something about that helped him see how important it was that he was still here, physically and mentally. He could recognize the plights of others, those just like him or even worse off. It suggested, maybe, a new direction for his life.

That sense was deepened after a visit from a Marine veteran named Mike Jernigan. He had lost his eyes in 2004 to a bomb in Iraq, and he stopped by Castro's room about two months into his stay at the hospital. Jernigan told Castro that after his injury he thought his life had ended, too. In addition to his eyes, Jernigan had lost most use of his right hand, a great deal of his face, and -- in time -- his wife, his childhood sweetheart. But Jernigan was healing. He traveled, raising money for guide dog associations, giving motivational speeches. Now, he showed Castro how to walk with a cane, and he answered any questions Castro had about life after blindness, primarily that big one, about what kind of a man he could be.

Castro's body had been on the mend, but it wasn't until then, seeing that even in the darkness Jernigan had found a good life, that Castro's soul began catching up. That should be me. A few days later, Castro overheard a nurse and doctor talking about the Marine Corps Marathon they'd just run in D.C. He decided to run it the next year; it seemed like the sort of outlandish goal that could show others that as brutal as his wounds were, his life would be his own for as long as he lived.

His room became a tiny gym, weights piled in corners and resistance bands strung from bed rails and walls. His time with Katie the Physical Terrorist became only a third of his workload. He felt his way around cardio machines. Evelyn and her mother guided him through weights.

After he was discharged from the hospital in early December, nearly three months after the mortar attack, his wife and her mother drove him to the gym near their home in North Carolina. Evelyn quit her job as a speech-language pathologist to help him. Until he was finished with recovery, the Army couldn't discharge him, so they got by on his military paycheck. She handled his appointments, laundry, cooking. She bathed him. When bits of shrapnel came to the surface, she squeezed them out for him. The couple kept them in a glass jar. She chauffeured him to the gym and, later, races. At first he couldn't figure out how to run. Ellipticals and bikes were stationary, but running, even on a treadmill -- he had no feel. He fell often. Finally, a friend he made while at a Veteran's Administration blind rehab facility in Virginia suggested he and a guide use a shoelace. Back in North Carolina, shoelace in hand, Castro started running with some buddies at a Fort Bragg track. They started with 800-meter runs.

In a month or so, 800 meters became a mile, and a mile became two or three, and from there it was just a matter of conditioning and pace, same as anyone. Sometimes he'd fall and twist an ankle or bang a knee, and his friends would ask if he was good to keep going. He'd laugh.

"Man, if pain could stop me, I'd already be dead."

He had had more than 40 surgeries. Some days everything hurt, and yeah, he wanted to quit. But then he'd think about Dreese and Porras. He became relentless, and Evelyn worried. She'd suggest he take a day off. He'd argue, "I can't. If I'm going to come all the way back, and stay back, I can't f------ back down." Training had become what morphine had once been. In the gym and on the road, all the stress and anxiety he felt about his new life sweated itself out. "It was like my fix," he says.

Castro ran the 2007 Marine Corps Marathon, almost a year after the mortar attack. Three people ran with him. Unable to keep pace, one fell out at 10 miles. The other at 20. Castro finished in 4:14.

Seeing what he could do, he wanted to do more. He ran more marathons, rode long bike rides ranging as far as 400 miles, even did some triathlons. (He'd swim tethered to someone leading him; he'd bike on a custom-made Cannondale tandem.) The Army also decided not to discharge him, instead making him an executive officer with the HHC 7th Special Forces group at Fort Bragg. Out of combat but involved in most everything leading up to it, Castro became the only known blind active duty Special Forces officer in Army history.

Evelyn couldn't deny it -- for awhile, she found it all rather exciting. She felt like she was on one of his missions with him, for the first time ever. He called her his pit bull and a workhorse. She tried her best to love and to endure, and she figured that after a year or two, he'd have it all out of his system. Then they could settle into a new life, maybe have a baby.

But that didn't happen. Something was starting to erode between them.

AROUND MILE 13, Castro pops 500 more milligrams of Tylenol and about as much Advil. He and Sullivan walk hills, keep steady pace on downhills and flats. They hit every water stop. Every time someone is spraying runners with a hose, they soak. They run part of the race with their shoes full of water.

Disaster nearly strikes at Mile 18, where earlier in the day last year's winner succumbed to the heat. A pack swerves in front of Castro, stops dead for water. No time to pull the tether and explain -- Sullivan grabs Castro's hand, yanks him aside.

"I really feel something there," Castro jokes, "when you hold my hand like that."

A couple of miles later, a runner collapses from exhaustion, and Sullivan does it again.

"Still feel it?" he asks.

"No, I lost it."

A few moments later, looking to pass the time, Castro starts singing, "She Lost That Lovin' Feeling." Sullivan laughs and before he knows it, finds himself singing along. They belt it out, and for a while the heat doesn't seem so bad.

IN 2008, Castro met 20-year-old Joel Tavera. Five rockets had blown up Tavera's Humvee in Iraq, and he was one of two survivors. He had third-degree burns all over his body, went blind, lost part of a leg, and his hands quit working right. The Navy contacted Castro, and he flew with Evelyn to San Antonio, where Tavera was in intensive care. He was missing part of his skull -- removed by doctors because his brain was swelling -- and most of his skin. Castro couldn't shake Tavera's hand; what was left of it would have fallen off. Castro, of course, couldn't see him, but Evelyn could. That she didn't say anything upon meeting him told Castro everything he needed to know.

"It was devastating," Castro would later say. "At least when I lost my sight, I was already 39 -- I had lived a life. This kid had not lived his life. So he'd just given up on his life."

Tavera grew addicted to painkillers after his release and gained 50 pounds. He had to undergo countless more surgeries and Castro would visit him at the hospital, offering encouragement. Castro flew to Tavera's home in Florida to talk with him, too. Soon they were speaking on the phone almost every day, and the message from Castro was the same: You can still lead your own life.

The message ultimately broke through. In 2010, Tavera ran a 5K. Last year, he ran three.

"Just knowing what he'd been through," says Tavera, "and seeing that he could do all these crazy things he's doing, after all that -- it showed me that maybe I need to not let my condition get me down so much, too. It sucks sometimes. But then I talk to him, and I just think about what he's been through, and I feel like yeah, I can keep going. At least for another day."

Tavera was not the first guy Castro met with -- and he wouldn't be the last. There are dozens of wounded veterans whom Castro has mentored. And thousands more who've heard him speak. Castro began seeing these visits and those speaking engagements as his destiny. A soldier to the core, his new life served the same purpose he'd always lived for: To fight for the good of the world. Thousands of soldiers come home broken by war, and they face their own dark painful nights, their own horrific battles. To Castro, they were now all his guys.

He gets them laughing with jokes about, say, his nose. "God takes a rib out of Adam and gives him Eve. All I got was a nose?" He tells them about Walter Reed, where, as he puts it, "I should've died. I was seen by every damn clinic there, minus OBGYN and labor delivery." He shows his scars. He has people run their fingers over the shrapnel embedded in his skin, and tap his cheek, which was rebuilt entirely from plastic. He listens to their stories, and he tells his.

"Ivan has made me feel like, with as serious of injuries as he's had, that anything can be possible," says Sgt. Ken Katter, who suffered neck, back and brain damage in Iraq after an improvised explosive device detonated beside him in 2007. He also finished a 5K in 2009, after meeting Castro. "I might not be able to do some of the things he can because of my injuries, but I can do something. And doing something, anything, is better than doing nothing."

Castro soon spent half the year traveling. The training, the running, the speaking -- it became his life, and Evelyn's. This was no passing fad, as she had hoped. One year, he ran a marathon on her birthday. It rang more and more hollow, a blind man calling her beautiful. They didn't laugh together like they used to. The pit bull and workhorse jokes grew stale, then bitter.

She stopped traveling with him, letting him go alone with Dummar or whoever else would take him. Even without her, he kept going. In exasperation she'd ask, "Why do you KEEP DOING THIS, Ivan?"

His response was almost always the same: "Because I still can. Because people need to see what's possible."

They took a trip together in 2009, to the Grotto of Bernadette in Lourdes, France. Roman Catholic legend holds that its water heals all wounds. But not theirs. They talked and they fought and they cried. Ultimately, he told her that if she truly believed she deserved a different life with a different man, then she could go. The summer after the grotto, she left him.

AROUND MILE 23, Castro is struggling, and in a delirious reach for motivation, he starts singing the national anthem. Sullivan joins him, and then nearby runners do too. Everyone gets loud, and spectators join in, and as Castro runs, the song carries with him up the street. Even in the heat, he gets goose bumps.

IN 2010, divorced and in search of restoration, Castro cycled 400 miles across Europe with a big group. He and some other wounded veterans hung wreaths in Holland at the site of World War II's Operation Market Garden, at its time the largest airborne operation in history. Along the way, he met another cyclist named Amber.

She was an American, too, athletic, with fair skin, long brown hair and lovely blue eyes. Romance blossomed, then grew back in the States, where she worked in a confidential capacity for the federal government. "I've just had more adventures and have more fun with Ivan than ever with anybody else," she says. "And how can you not be inspired by him?"

In January 2011, Ivan and Amber ran the Disney Marathon together. That May, she accompanied him to Hawaii's North Shore Marathon, but didn't compete: She was pregnant. When she met him at the finish line, Ivan dropped to a knee and pulled out a ring. They were married a few weeks later in Maui, and she moved to North Carolina. That September -- just a few weeks after the attack's anniversary -- their daughter was born.

Soon after, he resumed his brutal schedule. Amber didn't question it: "When he goes and runs these marathons and gives these speeches -- I've seen people's faces, and how they're touched by him. I couldn't imagine saying, 'Don't do that.'"

Still, he was away for days or weeks at a time. "He keeps saying he's going to slow down," Amber says, "but I doubt that's going to happen."

THE LAST QUARTER MILE is easiest. The endorphins flood Castro's brain. A few minutes ago, he'd made sure to wipe the sweat and snot from his face, and now he makes sure to run with his head up, chest out. "It's all about the cameras now," he jokes to Sullivan. Beside him, Sullivan smiles. They run toward the finish, floating on the screams of thousands lining the sidewalk. With a few hundred meters left, Castro tells Sullivan, "Thank you."

They cross the finish line with a time of 5:44.

Amber is not there to greet him; she's home with their daughter in North Carolina. In two weeks, Castro will be away again, this time in Colorado Springs for the 2012 Warrior Games, a six-day competition for wounded soldiers and veterans. The month after he'll fly to San Francisco and spend two months riding a bicycle across the country. After that he's scheduled to run five more marathons before the new year, including the Marine Corps Marathon in Washington on Oct. 28. And in 2013, there's a 100-mile ultra he wants to do. In between, of course, are the dozens if not hundreds of soldiers to encourage.

It's a grind, and tonight, in Boston, he's starting to feel it. After finishing the marathon, he joined the veterans and police who were part of his convoy for dinner and drinks at a bar overlooking the Boston Harbor. Now, as he lays in yet another forgettable hotel room, he can't fall asleep. Although he's taken 200 milligrams of doctor-prescribed Celebrex, his knee, his hip, his heart -- they all still hurt. Lying in bed, aching in the dark, he wonders if it's still worth it. "Honestly, this is getting stupid," he says. "I'm killing my body. I'm running slower than ever."

Maybe it's the beers, or his exhaustion, but he is more frank than usual, more discerning.

"I'm always away from people I love," he says. "It takes such a toll on them."

Then he hears it -- that question: Why do you keep doing this, Ivan? He stiffens slightly, growing more resolute, as if he has decided something.

"'I will never quit,'" he says. "They're more than just words on a shirt."

Castro says one more thing before sleep finally comes. For the first time all day his voice is heavy, even solemn.

"That's just what a good soldier does. That's just what war is.

"You just hope everyone else will understand."

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