NORMAN, Okla. -- The answer to the great mystery of Lincoln Riley's ascending-at-warp-drive career arc is stored on a cell phone.

Before Oklahoma's Bob Stoops shocked the world in June with his retirement, it had already been sort of decided on this campus that Riley -- a 33-year-old assistant with zero head coaching experience -- would take over.

Never mind most of those making that momentous decision were probably thinking five years or more into the future. But they didn't blink when Stoops stepped down ahead of whatever schedule they had in their heads.

It had already been determined Riley wasn't a Lane Kiffin being gifted an NFL job before he knew what he didn't know. No last-name fame from his daddy opening doors.

Riley 's hometown is Muleshoe, Texas. His wife Caitlin is from 40 miles away in the equally tiny burg of Dimmitt.

Humble overshadowed hype every day.

"I would give up anything to be raised in a small town," Caitlin said.

But there is that existing mystery: Somehow, everyone from Stoops to the regents to the president already knew Riley would be next.

But why? Sure, there was the youth, the talent, the gobs of potential. Mike Leach made Riley a student assistant at Texas Tech at age 19. Four years later, Riley was a full-time assistant. At age 26, Riley was an FBS coordinator at East Carolina.

"Everybody was being critical when I named him offensive coordinator," said Ruffin McNeill, the former East Carolina head coach who is now Riley's defensive tackles coach. "Don't worry about how old he is. I got enough gray for he and I. You'll see."

It's McNeill's cell phone that begins to unravel the mystery of the boy king. On it he still keeps the recorded advice of a man who died 18 months ago.

"I've saved every voicemail, every email, every text. I listen to his voice," McNeill said.

Take a look at McNeill's Twitter page. On it you'll find a picture of three blood brothers -- McNeill, Riley and former Oklahoma athletic director Donnie Duncan.

Duncan passed at age 75 in March 2016. For 40 years, he was a coach, administrator and -- in one of his final positions -- senior associate commissioner of the Big 12. The job might as well been called Head of Institutional Knowledge.

He practically was the Big 12. It was he and former Texas AD DeLoss Dodds who shaped the new conference in 1994, flying to New York to meet potential advertisers. The league literally came together when those advertisers determined they could sell a lot of Chevy trucks in the Great Plains swath from Iowa down through Texas.

Duncan spent a large part of those four decades as a mentor. In his later years, he was heavily involved in the league's professional development initiative for the league's assistant coaches.

For what is still not a fully understood reason, Duncan took Riley and McNeill under his wing in 2009 when the coaches were together at Texas Tech. That year, Red Raiders assistant Charlie Sadler, who worked under OU's famed Barry Switzer, had told Duncan about them.

Remember, Tech was a rival of OU. Mike Leach was about to be run out after a widening scandal regarding his treatment of a player and the kid's annoying helicopter dad.

"I'm thankful Donnie saw his two little granddaughters grow up [before he died]," Riley told CBS Sports. "I'm really thankful he saw me come to Oklahoma. It was so special for him. …

"Up in heaven, if he's able to see Ruffin and I here at Oklahoma, he's up there smiling."

It's logical to suggest Riley wouldn't be here as the nation's youngest head coach without Duncan. When Stoops went out looking for a coordinator to replace Josh Heupel nearly three years ago, the search centered quickly on Riley.

According to a high-ranking school source, it was Duncan who said at the time that "Lincoln is our future coach."

Not next coordinator, next head coach. At the time, Riley was 31, calling plays for McNeill at East Carolina.

"He became more than [a mentor]," McNeill said of Duncan. "He was like a dad. I was more like his son. I'm sure he thought of Lincoln the same way. We became very close to him and his wife Sally. We thought of them as family."

Riley shared that sentiment. "I remember Donnie called me, 'If I can help in any way, let me know,'" he recalled. "… He came out for games, counseled us. Anytime I was in Texas, I would stay with him for a couple of days. The relationship … really, really grew to a father-to-son relationship."

It was an unlikely trio -- Duncan the sage, aging power broker fighting cancer; McNeill, a 30-year veteran coaching at his Group of Five alma mater; and this … kid, Riley.

Duncan began advising both on their contract negotiations, career choices, compliance, dealing with boosters, even coaching the pair up on how to deal with the media. They realized Donnie Duncan was grooming them.

But again, why?

"I have a saying," McNeill said. '"Real recognizes real and game recognizes game.' Lincoln is as real as they come. They know with me. What you see is what you get."

A week after replacing Stoops, Riley brought in McNeill to be his assistant head coach. Donnie's prodigies were reunited.

Oklahoma is perhaps one of the top five jobs in the country. The only comps for someone this young taking over something this big stretches back more than 60 years. https://www.cbssports.com/college-football/news/inside-college-football-few-comparisons-to-lincoln-riley-taking-over-oklahoma-at-33/

In the second game of his head coaching career, Riley is facing the biggest game of his coaching career. No matter how he got here, his experience, reputation and future will be shaped by how No. 7 Oklahoma plays at No. 2 Ohio State on Saturday.

Riley is more than confident.

"There is something about playing on the road that is just the best part of college football," he said. "I've just always enjoyed it more."

He'll get his chance against the Buckeyesm who won by three touchdowns here last season. The only hint of intimidation for the new guy is occupying his new office.

Riley is literally inheriting The House That Stoops Built.

At 1,800 square feet, it lacks only a throne. The office features a fireplace, high ceiling and enough fine wood crafting to be its own furniture store.

"I told Lincoln, 'If it ever gets slow in fundraising, we might have to rent your office out on Sundays for church services,'" AD Joe Castiglione said.

"Sometimes I wonder what the heck I'm doing [in this office]," Riley said. "… When you're here by yourself, it just echoes. It's too big for one person."

In that way, the office itself is just like the OU job.

Let's be honest: Riley immediately meshing with quarterback Baker Mayfield had a lot to do with him being the coach. Oklahoma went to the College Football Playoff in Riley's first season (2015). Last season, Mayfield was a Heisman Trophy finalist.

The quarterback this week considered that his coach was an offensive coordinator at roughly the same age he will leave OU.

"I can't even imagine myself having that power at that age," Mayfield said. "That basically would be me next year coaching Michael Crabtree."

That quarterback-coordinator relationship may have goosed Riley's head coaching prospects more than anything.

But during that time, Duncan also died.

"I consulted him on every major career decision," Riley said. "I think he saw something in us that he liked. We were smart enough to listen to him. His mind for college football is a treasure. He would predict things that would happen before they did. He could always see two or three steps ahead.

"Toward the end of his life, it was something that kept him going. We were his project."

In December 2015, Duncan was given the National Football Foundation Legacy Award in New York. The annual dinner is the Academy Awards of the sport.

On Dec. 8, 2015, Riley departed New York at 5 a.m. for Little Rock, Arkansas, to accept the Broyles Award given to the nation's best assistant coach. He made sure to be back in the Big Apple that night to see Duncan accept his lifetime achievement award.

It was one of the last times they saw one another.

But maybe this was destined to be all along. The man Leach described being cut from Texas Tech's roster made the right decision in 2003 to become a student assistant.

"I had to get rid of two [quarterbacks] to make the roster fit," Leach said. "Lincoln was one I was going to get rid of, for sure. I bring him in and I cut him. I'm thinking, 'It's going to be real easy, and it's going to be easy hiring him as a student assistant.' He wasn't real happy."

Riley, who remembers everything, "doesn't remember it that way." Leach told him to take the weekend to think about making the switch. Riley considered his quarterbacking future with a surgically reconstructed shoulder leftover from high school.

"I never was one afraid to grow up early," Riley said. "I came back that next Monday and told him, 'I'm in.'"

McNeill and Riley both long for a conversation with Duncan this week. He'd know what to tell them about a big-game prep, what to say to the team on Friday night, how to get that elusive road win that Riley loves so much.

All three of them used to relax on Duncan's 37-foot boat docked on a lake in Grapevine, Texas. Forget "boat," it looks more like a yacht. When his time was near, Donnie practically bequeathed the ship to McNeill.

Forget that McNeill had never piloted a boat and had no clue how to get it cross country to North Carolina. Duncan didn't want the craft to go to a stranger, so McNeill bought it, took lessons and eventually had it docked in Pamlico Sound near Washington, North Carolina.

"That last year at East Carolina was so stressing," said McNeill, who was fired after the 2015 season. "That boat saved my life."

That's what it was meant to do. When McNeill suggested to Duncan the new name of the boat would be "D.D." to honor him, the mentor balked.

"When you got on it," Duncan said, "That should be your timeout away from everything."

From where "The Timeout" is docked now, the Atlantic Ocean is easily accessible. From where McNeill and Ruffin are now, they still ask themselves the hardest question: Why did Duncan pick them?

"I've always kind of wondered that a little bit," Riley said. "I think he saw something in both of us that he liked."