So William Greer was really hurting, in that very particular, very painful way known only to Boston Marathon rookies, the hurt that comes from taking the first half too fast and getting hammered by the Newton Hills, and he kept wanting to walk.

"How far is the 24-mile marker?" he asked. The 24-mile marker was about 20 yards ahead of us, but William couldn't see it because William is legally blind, and he was asking me because I was running next to him (or, just ahead of him and to the left, because he has some peripheral vision on that side) as his guide.



"Just up ahead," I said.



"I'll walk when we get there," he said. And when we did, he did.



It wasn't William's best day. He had hoped for a 3:45 finish, and if not that, better than his 3:50 PR, or at the very least under 4:00, and all three goals had slipped away between leg cramps and stomach cramps and general fatigue. I said to him, "William, it's your race, and it's your day, and it's your first Boston, so just crossing the finish line alive is a win. But I want you to try to run that last mile. The last mile of Boston is a great thing, and you don't want to be walking it."



And William, who had conquered a brain injury at 17 that robbed him of his sight and almost his life, and gone on to live and work and marry and run six marathons (sans guide) and qualify for Boston, gritted and walked and jogged and got himself to mile 25, and started running, and started hurting even more, and as we approached the right turn onto Hereford Street, he said, "When we get to that turn, I'll need to walk again."



But he didn't. We turned onto Hereford and William didn't stop. He danced around a traffic cone like a man sighted and took the left turn onto Boylston like a man reborn, and as we ran that famous interminable canyon to the finish I kept urging him on as I waved my arms to whoop up the crowd, shouting, "A quarter mile! Three hundred yards! Two hundred! Can you see it yet, William?"



"Yes!" he yelled, and we crossed the line in 4:04, and I was as proud of him as I've been of anyone I've ever known, and happier with this marathon – my slowest – then any other I've ever run. I told him he could stop running – he hadn't realized he'd crossed the line – and I put my arm around William and enumerated his praises and we shuffled, slowly, into the finishing chute.



"You need some water?" I asked William.



"I don't want anything," he said, "Until I get that medal."



BOOM. An enormous noise, like the most powerful firework you've ever heard, thundered from behind us. We all turned to look, even William. Another BOOM. White smoke rose in a miniature mushroom cloud into the air, a hundred yards away, just on the other side of the finish.



"What the hell was that?" said someone.



I had just finished my tenth marathon, my third Boston, and I had never heard anything like that. Ever. Cowbells, music, cries of pain, sure, but never that.



"Keep moving, please," the officials shouted through megaphones.



I was curious. But I also had a very tired runner whose brain couldn't process the information his eyes gathered, and I was responsible for him, so I led him through the chute, helping him pick up snacks, sports drink, and yes, his medal.



The volunteers and officials looked fraught. Somebody told me it was a car bomb. Somebody told me it was in a building. Somebody else guessed it was an electrical transformer going up.



By the time we exited the finishers' chute and headed to the rendezvous point for the rest of our team, we knew it was something bad. Ambulances and cops were racing through the runners' meet-up area. Cops, clearly in the grip of an emergency, were screaming at us all to get the hell off the street, which we were supposed to own today. I got William to our meeting point safely, but his wife wasn't there. He started to worry. I started to worry. We tried to call her, but my cell phone wouldn't connect to anything.



Our team leader was hearing bad news. That it was a bomb. That there were injuries. That the race had been halted, leaving his runners – half of whom were blind – out on the course with nowhere to go. He was trying to organize rescue expeditions, get messages to lost runners. I got a call from my employer, NPR, asking me to go live on the air and describe what I had seen, what I could see now.



I walked down back toward the finishing chute, or where it had been. In the half hour since I had collected my medal, it had all been cleared away – no tables, no volunteers, no water trucks. Just the barriers, now intended to hold the media and the public at bay. I described to Robert Siegel the explosion I had heard, the smoke I had seen, the vast crime scene I was now seeing before me.



I returned to the meeting point. William was embracing Ellen, his wife, and in the mist of the growing chaos we posed for one last proud picture together. They headed off to their hotel, and I started on my trip back to my uncle's apartment, normally a 15-minute subway ride or 30-minute walk away. That day, it took almost two hours.



As I left Copley Square, I came across an amazing and terrifying sight. Beyond the barriers the police had set up, keeping everyone – not just runners – away from the finish line area, I saw ambulances. Dozens of them, maybe a hundred, lined up, lights on, engines running, ready to go. It was the same terror you might feel seeing an invading army ready to launch... except instead of promising horror to come, it demonstrated that a horror had already happened.



It only occurred to me, much later, as I viewed online videos of the bombing, how important William's gutsy last mile really was. We crossed the line at 4:04. The bomb went off as the clock read 4:09. Five minutes later. Which might well have been the five minutes that William would have needed to walk that last miserable mile, had he given in to the urgings of his hip, gut, and mind. But he ran the bravest and toughest mile of his life, not even able to see clearly what he was doing, just because he wanted to be able to say he did it, and by doing so, he crossed the line alive.

Sagal received the following message from William Greer on Tuesday:

"I have really sore legs. I am ready to start training for the next marathon, and I'm going to have a lot more long runs. I had the speed, I just need to really increase my endurance. Thanks very much for being my sighted guide; you made the marathon a great pleasure. The only problem were the bombs."

Peter Sagal, host of the NPR show "Wait Wait...Don't Tell Me," writes Runner's World's Road Scholar column.

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