Some young bands dream of the day they’ll write that one song — a beautiful, searing bundle of truth that persuades parents to have kids, inspires armies to stop fighting, and conjures puppies and kittens from thin air. If they’ve already written it — like, say, Foghat with “Slow Ride” — they probably remember the day it spilled forth as a momentous occasion, one on which it became clear that pursuing a career in music might be worth the trouble after all.

Spencer Smith, drummer of the Las Vegas–based emo-rock band Panic! At the Disco, probably has this dream. But it’s not the first thing that comes to his mind when you ask the 18-year-old whether he remembers that initial spark of possibility. “It was probably our first-week record sales,” Smith says over the phone from Great Britain, where Panic are on tour with another emo outfit from Chicago, The Academy Is . . . Saturday night the joint tour hits Avalon with Acceptance and Hellogoodbye, and Tuesday it’s at Lupo’s at the Strand in Providence. “Our record came out on the first day of our tour with Fall Out Boy,” the drummer continues, recalling that fateful Tuesday last September when A Fever You Can’t Sweat Out arrived in stores stores courtesy of Fall Out Boy leader Pete Wentz’s Decaydance imprint. “And our original goal was about 5000 copies that week. But we actually sold 9700, which was amazing. Then recently we had our biggest week yet coming up to Christmas: over 20,000 records. The week before Christmas is big for the whole record industry, but the week after Christmas everything slows down. The Panic record was the only record that went up.”

Panic! At the Disco are part of a new breed of young, smart, industry-savvy bands who, in an irony not likely lost on emo pioneers like Guy Picciotto of Rites of Spring and Fugazi, are colonizing emo-land, that former wellspring of self-important artistic and economic integrity. Along with The Academy Is . . . and a handful of other outfits, Panic are redefining what it means to be a rock band in a music industry shaken by file sharing, CD burning, consumer apathy, MySpace surfing, and radio acts that aren’t really rock bands at all. Panic are incredibly ambitious, surprisingly cynical, and mildly ruthless.

And they’re making some pretty good music. A Fever You Can’t Sweat Out, which Smith and his mates wrote and recorded after Wentz had signed them to Decaydance, is great fun. In the current issue of Rolling Stone, Wentz the A&R man (who is barely distinguishable from Wentz the musician) hypes the disc as sounding “like the Killers meets Fall Out Boy meets the Faint,” a handy little description that suggests he should try his hand at PR if he ever tires of FOB. The equation is just right: taut, catchy emo tunes tricked out with soaring keyboards and propulsive dance beats. Like all emo frontmen, singer/guitarist Brendon Urie writes lyrics dense with self-reference and wordplay. “Well, we’re just a wet dream for the Webzines,” he sings in “London Beckoned Songs about Money Written by Machines.” “Make us it, make us hip, make us scene.” In “Nails for Breakfast, Tacks for Snacks,” over surging guitars that conjure vintage Duran Duran, Urie describes being “prescribed pills to offset the shakes, to offset the pills you know you should take.”

More dependent on the sort of tried-and-true guitar-band verities that turned Jimmy Eat World into a mainstream sensation five years ago, Almost Here (Fueled by Ramen), the year-old debut by The Academy Is . . . , isn’t as sly or as distinctive as Fever. But singer William Beckett isn’t overrating his skills much in “Season” when he boasts that “I’ll sing you something you won’t forget.” And with nearly 100,000 copies of the album sold so far, it’s clear the band are connecting with fans. Over the phone from London, 21-year-old guitarist Mike Carden estimates that at least 300,000 people own the album thanks to uncounted illegal downloads and bootleg CDs. (At press time, the band’s MySpace page counted 116,111 “friends,” which suggests that Carden is right about at least 16,111 of those unauthorized albums.)

“The whole scene for us has blown up in a weird way that we didn’t really expect,” Carden says of the buzz surrounding Academy and Panic. “To be honest, when William and I were writing Almost Here, we had no clue. It was a record that was done in three and a half weeks. And now here I am in England talking to you about its success. It’s pretty surreal.”