IN AN NFL in which rosters are built on scouting reports, painstaking video dissections and gaggles of middle-aged men holding stopwatches, an underdog success story like Siemian's isn't supposed to happen. And it probably wouldn't have if fate hadn't allowed Kubiak a rare chance to channel-surf one fall Saturday night.

It's Nov. 15, 2014, and Siemian's disappointing senior season at Northwestern is nearing an end with a visit to No. 18 Notre Dame. His team is 3-6 and needs to win out to be bowl-eligible. In his only year as a full-time starter -- he'd platooned with Kain Colter the previous two seasons -- Siemian knows his already slim chance of impressing NFL scouts is fading to nothing. It's hard to imagine playing in the NFL when two weeks earlier he'd finished a 48-7 drubbing at Iowa on the bench.

But Siemian is stoked to play in front of 80,000 Fighting Irish fans and on national TV. He keeps his focus as the Wildcats fall behind. "He was just like, 'All right, we'll get the next one,'" former Northwestern offensive lineman Hayden Baker says now.

Sitting in Baltimore, Kubiak is enjoying the bye weekend and a rare Saturday night off as the Ravens' offensive coordinator. There are other games to watch -- Alabama leads a nail-biter at No. 1 Mississippi State, and Kubiak's alma mater, Texas A&M, is about to kick off with Missouri -- but even though the Wildcats trail 40-29 with just five minutes left, Kubiak doesn't switch the channel. Instead, he watches Siemian hit a clutch pass over the middle for a big first down and then scramble right for another. From the 6-yard line, Siemian tucks the ball and runs for a touchdown. After a turnover, he finds Kyle Prater on a quick route for 17 yards to help set up the field goal to tie the game. The Wildcats go on to win in overtime 43-40.

The next morning, Kubiak strides into the office, where coaches are making small talk about what they did Saturday night. Still struck by Siemian's poise, he asks, "Did anybody see the quarterback from Northwestern?"

The next week at Purdue, Siemian continues to impress anyone watching as the Wildcats cruise to an early 21-0 lead. Then in the second quarter, he runs a quarterback sneak on fourth-and-1. But Siemian gets stuffed short ... and doesn't get up. By the time Siemian is placed on the trainer's table, Baker knows his roommate has torn his ACL. Northwestern holds on against Purdue but plays its final game of the season without Siemian and loses to Illinois. The bowl hopes are gone; for Siemian, everything seems over.

"I wonder if I'll ever play football again," Siemian tells his family and friends.

His surgery in early December is a success, and Siemian spends the next few weeks recovering in Illinois. He visits coach Pat Fitzgerald's office and says he is thinking of giving up football. "No, man, you need to train," Fitzgerald remembers telling him. "Your best football is ahead of you."

Siemian hears the same message from one of his mentors, a guy named Steve Schnur. About 20 years earlier, Schnur had far more success quarterbacking Northwestern than Siemian ever did, winning back-to-back Big Ten titles. But his smaller frame didn't appeal to the NFL, and Schnur didn't get invited to any camps. He instead became an exec with Duke Realty.

Siemian had interned at Duke Realty the summer before his senior year and was, by all accounts, a natural -- personable, a fast learner, trustworthy and never stressed by any projects he was given. "He's got a presence about him," Schnur says. But when Siemian talks to him about giving up football, Schnur offers no sales pitch for real estate. He says that the corporate world can wait and that if he has even the slimmest shot at the NFL ...

"Go for it," Schnur tells him. "The NFL will move on quickly from you."

While the stars of the class of 2015 go to the combine, Siemian begins to rehab his knee. His name isn't even on a long list of quarterback prospects handed to Kubiak when he becomes the Broncos' head coach that January, instead relegated to a pile labeled "others." Kubiak asks and is told that Siemian tore his ACL.

"There were some people concerned about his health," Kubiak says now. "So it was a matter of just saying, 'Hey, this kid's got a big league arm. He's very bright. Let's just do some homework on him.'"

Siemian isn't healthy enough to work out at Northwestern's pro day on March 3, but a few weeks before the draft he holds his own workout. Kubiak dispatches passing-game coordinator and QB coach Greg Knapp to Evanston for the April 9 session. He is the only coach who shows up, along with reps from a handful of other teams, to watch Siemian essentially throw on one leg.

Knapp likes to take a player out to dinner the night before his workout and has a lot of questions to resolve that night. Is Siemian sharp enough? Will he be a fit in the quarterbacks room? It's a unique situation. Siemian won't just have to keep up with the coaches; he'll have to keep up with Manning.

Knapp loves the kid's answers and instincts. The workout the next day leaves him even more encouraged. "He couldn't do a lot of mobile stuff," Knapp says. "But he could drop straight back and throw the ball, and I could see how it came off his hand and see how tight the spin was and what kind of arm strength he had. It really showed up in person that this guy's a natural thrower."

So Siemian, via luck and a decent workout, wins the Broncos' interest -- enough to warrant the 250th pick in the draft. The team that shows the next-most interest, according to Fitzgerald, is Cleveland, which has him in for a visit two weeks before the draft. Think about that: Trevor Siemian could have wound up in the city where quarterback dreams die.

LANDING IN DENVER really is a dream scenario: the opportunity to learn from Manning, a legend in his final season, and a quarterback brain trust of general manager Elway, Kubiak and Knapp. He's No. 3, behind Manning and Brock Osweiler, Manning's heir apparent. No pressure and plenty of space to grow.

Siemian doesn't like to talk about his relationship with Manning. It's almost as if detailing what some describe as a friendship -- Siemian's family says the two are golf buddies -- would be disrespectful. But there clearly is warmth between the legend in his final season and the long shot in his first. When Siemian has a question, no matter how small, Manning always seems willing to help.

"Peyton was an awesome example for me," Siemian recalls, "for how to not just play quarterback but how to operate every day. How to be a teammate and how to be a leader in the locker room."

It doesn't take long for them to connect. Manning is funny and sarcastic and likes to throw digs at his coaches and the younger quarterbacks over the course of a meeting. In one of Siemian's first QB sessions in Denver, Manning zings him, and he zings right back. Knapp can't say what the barb was, but he says it told him a lot about Siemian. "It was like, 'All right, this kid's not just going to follow the lead,'" Knapp says. "'He's going to be a leader.'"

C.J. Anderson says Siemian and Manning share some personality traits, including that sense of humor. (His college teammates call Siemian a goofball and tell of the time he misplaced his helmet and then ran to the huddle, yelling, "I'm coming, boyyyyyys!")

"Peyton was a serious calm," Anderson says. "Trevor is more of a funny-comedian calm. He's kind of like Peyton. In between those lines, it's business. Outside of it, it's all fun and games."

Asked the biggest lessons he learned from Manning, Siemian comes up with a lot of variations on this theme: Manning taught him how to approach the game Monday through Saturday, how to be prepared.

"I was very fortunate to be able to share the room with him," he says.

DENVER BEATS CAROLINA in the Super Bowl as Siemian stands and watches. The whole world assumes that Manning will retire, maybe right there on the field. On March 7 he makes it official. Two days later, the real thunderbolt hits: Brock Osweiler is not sticking around. He takes a $72 million contract and leaves for Houston.

Siemian -- as is his nature -- doesn't remember where he was when Knapp called him with the news. On the phone, Knapp tells him the Broncos will add some quarterbacks but reminds him that Kubiak will play the best man, regardless of financial commitment.

"All right," Siemian tells him. "That's all I needed to hear. Let's go."

An old teammate sends Siemian a text, "QB1," as a joke. And in early March, the truth is that such a message does seem kind of hilarious. Very few general managers would've taken the risk Elway did in letting Osweiler walk to Houston. The outside world screams, "What is Elway thinking?"

But Elway knows what he has with Siemian in the mix. "The coaches really liked how he handled the classroom and how he studied and picked up the offense," Elway says today. "But until you see him under the lights, you never really know how they're going to react. Until he gets in there, you never know."

"My mentality going into everything is, 'I'll be damned if I'm not prepared for whatever comes my way,'" Siemian says. "I'm going to do whatever I can to be ready for it."

The Broncos end up drafting Paxton Lynch in the first round and trading for journeyman Mark Sanchez, but neither can beat out Siemian by the end of preseason. Denver will begin defending its title in a rematch with Carolina.

Elway couldn't ask for a brighter spotlight for his young quarterback.

ON THE SIDELINE before the marquee NFL Kickoff game, Siemian stands calmly with his hand on his chest during the national anthem, while across the field Panthers linebacker Luke Kuechly is so amped to hit him that he bounces and sways through every bar of the song.

On the Broncos' first play from scrimmage, Siemian wants to throw a quick screen, but a defensive end jumps right into his throwing lane. Instead of trying to throw it over the defender, Siemian pump-fakes and sidearms the ball around him.

Elway is put at ease.

"For a guy taking his first snap in an NFL game to be able to readjust and make that play really showed us something off the get-go," Elway says.

The Broncos eke out a 21-20 win. On Oct. 24, Elway's decision to go with Siemian is put to a more binary test when Osweiler and the Texans come to Sports Authority Field at Mile High on a Monday night. Things do not go well for Osweiler. Seven months after the city fretted over his departure and who'd replace him, Osweiler is consistently booed as he fumbles three times, losing one, and throws for just 131 yards in a 27-9 loss. Siemian throws for 157 yards and a score, but more important, he avoids mistakes. Good enough.

His coach and general manager know not to measure Siemian's performance by box scores. "He's done a tremendous job up to this point," Elway says. "He's only going to get better."

And his teammates, who chose him as one of three midseason captains, know it too. "Trev is my guy," linebacker Shane Ray says. "What happened with Trev, nobody expected that."

Not even a certain coach who was channel-flipping on his couch in Baltimore.