My My roommate, David Millar, was telling me how easy it had been to become one of the most famous ex-dopers in cycling. We were having a beer this past February in a crowded sushi bar in downtown Santa Clarita, and he had to speak loudly. Many of the patrons had watched the exciting finish of Stage 6 of the Tour of California that afternoon, and they were in a festive mood. Some recognized Millar—perhaps because he'd nearly won the stage and was in second place overall, or perhaps because he's one of the defining cyclists of the modern era, both for what he did in the past and what he's doing today. "I know I have a responsibility," Millar told me, taking a sip of his Kirin. "I have to tell my story."

A year and a half into his return from a two-year suspension for using the blood booster EPO, Millar is racing for what may be the cleanest team in cycling, U.S.-based Slipstream/Chipotle. As a new team, Slipstream holds only a second-tier Pro Continental racing license, yet the squad has earned worldwide praise—and an invitation to the Tour de France, starting July 5 in Brest—for its bullheaded determination to race without drugs.

"Cycling has lost a lot of credibility," Jonathan Vaughters, Slipstream's general manager and the architect of its revolutionary drug-testing program, told me between stages in California. "To rebuild, it needs to be 100 percent transparent." To that end, Vaughters had taken the dramatic step of inviting a journalist along for the Tour of California. Not just to ride in the team cars but to eat with the riders, sit in on meetings, watch the drug tests, and sleep in the same room as the team's captain. All he'd asked in return: Get a flu shot and don't snore. At my first dinner with the team, Chann McRae, a former pro and now Vaughters's second in command, had told me, "No one has done what you're doing. I mean no one."

So, every night, after Millar and his seven teammates raced against some of the world's best teams, after they got their massages and mounds of pasta, he and I would retire to the local Hyatt in towns like Solvang and San Luis Obispo. Sometimes we would watch TV, other times we would listen to music and talk. Millar, 31, is not a stereotypical jock. He's tall and lanky; Scottish by nationality and accent, though born in Malta and raised in Hong Kong; and he's as comfortable talking about the Sneaky Sound System (an Australian dance band) or his favorite Cormac McCarthy novel (Blood Meridian) as he is about cycling. His—our—door was always open, and other cyclists stopped by to chat or just hang out. It certainly wasn't like the old days, my roomie told me.

"You wouldn't know what your teammates were doing behind closed doors," he said, recalling his early years as a pro. "There were doctors going between rooms, bags of medical waste being taken out, soigneurs [team assistants] dropping off ice each night to put inside flasks and keep vials of EPO cold. Syringes were sitting out."

After dropping out of the 2001 Tour de France because of exhaustion, Millar—a gifted rider who had already won six races that year clean and had worn yellow in his first Tour—gave in and started taking synthetic EPO, a hormone that boosts the production of red blood cells. "I was too tired to fight it anymore," he told me. "It was time to dope. I thought, No one cares. I could get away with it, and it would guarantee results. Doping was easy."

Millar used EPO during three different periods between 2001 and 2004. He was conservative with his doses, always stopping them 12 days before any race, including the 2003 World Time Trial Championship (a title he won and was later stripped of). That was standard strategy for passing the screenings. There wasn't a practical test for EPO until 2006. So, back then, the best authorities could do was measure a rider's hematocrit level—the percentage of red cells in the blood—and it was easy enough to manipulate that by timing your injections carefully. Millar got caught only because French police, searching his apartment as part of a broader investigation into doping by members of his team, Cofidis, found two bloody, EPO-contaminated syringes. Millar was eventually cleared of any criminal charges in France, but his two-year racing ban was, at the time, the longest in cycling history.

"I spent the first six months drunk," he told me. "I didn't care if I came back. But then I started to realize that cycling was the only thing I was really good at. As a teen, I'd been so focused, ethical, driven. Now that was all destroyed. By losing it, I realized the thing I loved the most was cycling."

Millar started training again in 2005, determined to race clean, and signed with the Spanish team Saunier Duval. He resumed racing in the summer of 2006 and quickly became the go-to ex-doper for journalists. When he learned, during a press conference at last year's Tour de France, that pre-race favorite Alexandre Vinokourov had tested positive for blood doping, he blurted, "Jesus Christ. There you go, that's my quote." Then he broke into tears.

He wasn't the only one. Both casual and diehard fans have been giving up on the sport after watching decades of scandals and fallen heroes. Last year, after Vinokourov and presumptive winner Michael Rasmussen were bounced from the Tour—the latter after it was suggested that he had misled cycling authorities about his whereabouts in the weeks leading up to the race—the French newspaper France Soir proclaimed, "The Tour is clinically dead."

Slipstream is trying to do its part to resuscitate it. "Doping has to stop, and everyone has to prove it's stopped, or we won't have races like this anymore," Vaughters told me as we followed the peloton during Stage 6. "The sport won't survive."

Now all he and his riders have to do is convince the rest of the cycling world.