At this year's Grammys, during which artists from Katy Perry to Beyoncé sang earnest devotionals, Imagine Dragons staged a bold experiment in how to promote an album: They performed live in a four-minute TV ad for Target. Using 22 cameras, music video director Jonas Akerlund dramatically captured the band playing its soaring new single "Shots" in its entirety downtown in Las Vegas, the band's hometown.

Put off by the overt, well, commercialism of the clip (which cost about $8 million in airtime), critics sniped at the group online. But Imagine Dragons -- which memorably mashed up "Radioactive," its breakthrough mega-hit and 2014's best rock performance Grammy winner, with Kendrick Lamar's "M.a.a.d. City" on the 2014 telecast -- saw "Shots" leap from No. 99 to No. 26 on iTunes the next day. Interscope Geffen A&M vice chairman Steve Berman says, "We saw a big spike in preorders and awareness" for the group's new album, Smoke + Mirrors (out Feb. 17).

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"We're an atypical band," says lead singer/?songwriter and founder Dan Reynolds, 27, a week before the Grammys. "We're not tatted-up, trying to make a statement. The spirit of rock'n'roll is not that you're living on the edge, that you're a cokehead -- those are just lifestyle choices."

The most atypical thing about Imagine Dragons may be their towering success in an era where rock music struggles for a mass audience. (The name is an anagram of another name the group rejected, and now coyly refuse to divulge.) "Radioactive" sat on the Billboard Hot 100 for a record-shattering 87 weeks, and the band's 2012 debut, Night Visions, went double-platinum in the United States. Rock radio no longer makes careers. New bands that don't appeal to a specific segment of fans -- metalheads, say -- need top 40 radio to truly blow up. Only one other rock band has produced as many top 40 hits (three) since 2010: Fun (who, as Billboard recently reported, may be disbanding). "We have guitars and drums and bass, so people call us a rock band," says Reynolds. "But I love big, poppy melodies. And I'm not going to apologize for that."

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Its label's savvy strategy (Interscope persuaded -- yes -- Target to carry the unproven band's debut album) and some lucky timing ("EDM was starting to be big, and 'Radioactive' was an alternative song with dubstep," says Reynolds) helped fueled an explosive start for the band. But now Imagine Dragons must strike a balance between rock and pop while attempting to match an unexpected smash of a first album. The Grammys-ad gambit could have triggered backlash (think: U2's ill-fated freebie iTunes release). The response to, and sales of, Smoke + Mirrors will prove whether the band can truly help rock forge a new path.

Imagine Dragons consists of two pairs: the brooding duo of Reynolds and guitarist Daniel Wayne Sermon, 30, who can spend hours agonizing over a song mix through text messages; and the boisterous rhythm section of drummer Dan Platzman and bassist Ben McKee, both 28, who share a rented apartment. On Twitter, Reynolds tends to share broadly philosophical musings -- "I could spend a lifetime worrying about tmrw and yesterday. or I could live right now in the present moment-enjoying the feeling of now," he wrote on Feb. 11 -- that could appeal to virtually anyone. Indeed, Imagine Dragons fans, as he observes, come from all walks of life: "First it was college kids, then high school kids, then older people coming to our shows with their kids. Once you play on mainstream radio, you really get a lot of mainstream followers."

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The guys have an easygoing camaraderie. Over lunch one afternoon at Las Vegas restaurant Skinny Fats, Reynolds brings up the time McKee had to get bailed out of jail to make a concert. "Being naked on the Strip at night is not legal," Reynolds reminds him. "There were some bad choices being made," concedes McKee. "Vegas is a crazy place."

The group kept craziness at bay during the recording of Smoke + Mirrors. It bought a house in a sketchy section of Las Vegas -- multiple drug stash houses populate the block, reportedly -- and built a recording studio within. (When the bandmembers drained the hot tub in a corner of the studio they discovered that it produced an excellent ambient sound for the drums if they put a microphone inside of it.) The band spent six months plugging away from 9 a.m. to 5 p.m., tracking its progress on a whiteboard. The banker's hours allowed Reynolds and Sermon to go home to their families at night; Reynolds has a 2-year-old daughter, Arrow, and Sermon is father to a 6-month-old boy, River. "I don't like to go out; I don't like afterparties," says Reynolds. "I don't live a typical rock-star life."

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As a kid in Las Vegas, Reynolds wanted to be an FBI agent. When he heard police sirens, he would follow them to the scene of the crime. (Cops remains one of his favorite shows.) He also grew up loving masters of rock melody like Elton John and Harry Nilsson. When he sang, his brothers would tease him about his guttural voice. But he learned the drums, and at around 12 years old, stole his older brother Mac's microphone and began recording a cappella songs of his own invention.

"He was just a kid making videotapes with his brothers," says Branden Campbell, who plays bass for the band Neon Trees and grew up near the Reynolds family. "It was a very creative family. They would deflate a soccer ball, cut it in half and put it on their heads."

After high school, Reynolds, who was raised Mormon, went on a two-year mission in Nebraska, proselytizing for the church and helping drug addicts. He attended Brigham Young University in Provo, Utah, only to drop out and form Imagine Dragons. "It was an extremely hard decision for me to make -- I come from a family where academia is priority one," says Reynolds. After the lineup solidified, the band relocated to Las Vegas. The other three members all attended the Berklee School of Music; until he quit, McKee paid his tuition with financial assistance from a California state scholarship for talented chemistry students.

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The band took any gig it could find, even opening for a mime at a local mall. They also played six-hour sets three nights a week at a casino's bar and grill, mixing originals with covers of The Cure, Rush and The Beatles. "We picked bands we loved and studied the songwriting," says Reynolds.

One of the three EPs the band recorded got into the hands of British hip-hop producer Alex Da Kid (the man behind Eminem's "Love the Way You Lie"), who wanted to collaborate with Reynolds -- writing songs for other people. "I didn't realize it was just one band," he says of the EP. "I thought it was the best songs from different bands."

Instead, Alex Da Kid signed the band to KIDinaKORNER, his Interscope imprint, and executive-produced its debut. The group toured relentlessly, made a video for "Radioactive" starring actor Lou Diamond Phillips and a bunch of stuffed animals, and saw Night Visions debut at No. 2 on the Billboard 200. It remains on the chart after 127 weeks.

Reynolds acknowledges that the last couple of years have brought many wonderful things. But he has been "depressed as hell" for a while, and sees a therapist. "It's lonely when your life changes like this," he says. "I've lost all my friends. It's not like we had some blowout arguments or that I feel I'm too cool -- the relationships feel false. Anytime I'm talking to someone, I feel they're just thinking about Imagine Dragons." He sighs. "Probably a lot of them aren't treating me differently. I just can't get over it."

Reynolds' relationship with his wife, Aja Volkman, and their daughter grounds him. He met Volkman five years ago, when Imagine Dragons were opening up for her band, Nico Vega. He was immediately smitten when he saw her onstage, and waited hours after the show for a chance to talk to her. "We're both really weird people, but really open," he says. "Our first question was, 'What do you believe?' " Volkman had recently left Scientology; Reynolds was full of doubts about Mormonism. They became best friends who talked daily on the phone and secretly wrote songs together telling the story of their relationship. A year later, they were in love. "The experience was magical," says Reynolds.

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Although he was raised Mormon, Reynolds doesn't subscribe to all the church's tenets. "I don't necessarily agree with a lot of the culture that comes with it, but I still identify as Mormon," he says. "I like to think of myself more as a spiritual person." Reynolds has harbored these doubts since childhood; he used to write songs about them to play for his conservative parents, letting them know indirectly about his internal struggles. He comes from a large family, with seven brothers and one sister. "He suffered from some of the woes of being the seventh son," says Mac, who now manages Imagine Dragons. (Another brother, Robert, is the band's lawyer.) "That brought some insecurities -- it was difficult having older brothers who were valedictorians in high school."

The religious mission proved to be the most difficult work Reynolds would ever do. "I lived in the projects and would help mothers who were abused to get out of the situation or clean their houses before child services would come to take away their kids," he recalls. "It's super-heavy stuff for a 19-year-old." While he was never comfortable knocking on strangers' doors, being onstage has always felt natural to him. "A lot of time during the day I'll feel nervous, or have anxiety about talking to people," he says. "On-stage, I just don't."

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Backstage at the Mayan Theatre in Los Angeles, three days before the Grammys, Imagine Dragons wait to play a short set and announce their North American tour of arenas: 39 dates with Metric and Halsey, kicking off June 3 in Portland, Ore. The band meets a group of Southwest Airlines representatives: six women, mostly blondes. Imagine Dragons will play live on a Southwest flight; other partners on this album include Jeep, Riot Games and the "What Happens in Vegas" campaign. Two of basketball superstar LeBron James' commercials, for Beats and Sprite, feature the band's music. James recently retweeted a photo of himself wearing one of its T-shirts with the message, "Yes Sir my boys!! Keep being amazing!!"

Imagine Dragons first partnered with Target last July, for the brand's All-Star Concert in Minneapolis, pegged to Major League Baseball's All-Star Game. "We studied the Grammys, and people want more music," says Target vp marketing William White. "Everything about 'Shots' felt right for us." (Neither Target nor Interscope would say whether the band was paid for the ad.) "It never feels like an artistic compromise as long as it's about spreading the music," says Reynolds of the commercial tie-ins. He points out that cross-promotion exists everywhere: a song in a movie promotes the film, while a Grammys appearance helps the Grammys and CBS brands.

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Back in its dressing room, the band eats lunch. "Why do they say green apples are better for ?you?" asks Platzman. "They have lower sugar content," McKee immediately answers. This inspires him to share his recipe for gluten-free ?peanut-butter cookies. Platzman is gluten-intolerant; Reynolds has an autoimmune disease, and starch inflames his system.

The band hits the stage, hypes its tour and answers questions tweeted by fans. Asked where he keeps his Grammy, Reynolds says he put it in his daughter's room. The audience swoons. "I see my baby girl," he then cracks, "and tell her that she's second place to my Grammy."

The band plays for a half hour, and Reynolds visibly unstiffens. When he spots two fans whom he recognizes from gigs at The Viper Room five years ago, he thanks them by name. By the time the band finishes, with "Radioactive," Reynolds is howling and beating an enormous bass drum with a mallet.

Offstage, Reynolds is sweaty, but not completely satisfied. "I pushed too hard on 'Radioactive,' " he says. "Stupid." Still he says, toweling off, "I love a song that makes you feel like an explosion." If he feels comfortable onstage, maybe it's because it's the only place he can truly erupt.