It's an old show-biz truism (and the title of a wonderful early Rolling Stones' b-side): It's the singer, not the song. This week, "Rock Star:INXS" turns that phrase upside down. It's the song, not the singer (or to be more precise, Rocker) that matters tonight.

Right from the start, things are a little topsy-turvy. As the show opens, Dave shows up at the Mansion. His very presence leads Marty to conclude "something's up." And something is indeed up. Dave has come to explain this week's clinic, which is designed to test the Rockers' ability to collaborate on writing a song. And he has arrived bearing, if not a gift, something very special -- CDs and the sheet music of a new INXS song, for which the Rockers are going to write a melody and lyrics. They have one day to come up with them, and the winner, as judged by Dave and Andrew, will win a Q Line SLS surround sound system, designed by music legend Quincy Jones (both a friend and fan of INXS) and a night on the town with INXS. It's the clinic J.D. has been waiting for -- being able to sing a song he wrote before Dave and Andrew is "a dream come true."

As his extra reward for doing the encore last week, Ty gets first crack at whom he wants to work with. He chooses Marty, but instead of collaborating, Dave pulls a switcheroo and tells Ty that Marty is going to be his opposite number and lead the other team.

Sides are quickly chosen up (a process Jessica compares with gym class). On one team: Ty, MiG, Suzie and Deanna. The other: Marty, Jordis, J.D. and Jessica. Both teams quickly retire to their separate corners and get to work.

Ty's team starts by listening to the track -- a bright, propulsive rocker powered by an insistent guitar riff -- and find themselves immediately inspired. Bouncing to the beat, Suzie lights up, telling the others "I got ideas." Ty and MiG both have melodic ideas for the verses, including a stop-time hook for the chorus. Things are moving along swimmingly.

On the other side of the Mansion, Marty's team takes a more analytical tack, first picking out a musical director. J.D. nominates Marty, an offer he leaps at with alarming speed. For Jessica, this clinic will be her biggest learning experience -- especially since she reveals that she's only ever written six songs. As they get to work, it's clear that not everyone on Marty's team is on the same musical page. J.D. starts scat singing a few phrases over the instrumental track, which Jordis pretty much dismisses outright, calling them "a really obvious melody" (which is an odd complaint when you're writing a pop song. Some of the most memorable songs have tunes that are so obvious, so unerringly part of the musical fabric; it almost seems they have been there forever).

Ty's team gets along, having a great time working on their song. He's amazed at how much fun they're having, "acting like little kids."

Marty's team also acts like a group of youngsters, but the most apt term might be "childish." They've already broken up into cliques, something J.D. immediately notices. Marty and Jordis have become a tight little unit, he notes, worrying he might end up with "the short end of the stick." In the workroom, Jordis is quick to shoot down J.D.'s lyrical ideas, calling them "too specific" and "obvious."

To defuse the tension, Marty asks J.D. to continue working on his ideas in another part of the Mansion, stroking him by telling him he should work on his "genius lyrics." It's a nice variant on J.D.'s "killing them with kindness" strategy, and one that works -- J.D. strangely views his being shunted off to the side as being part of the group. With J.D. off to the side, Jordis and Marty are free to write the song they want to write. (Where's Jessica, you ask? Her contribution to the seventh song she's ever written appears to be staying out of the way.)

Bliss still reigns with Ty's team, as they fine-tune their song, titled "Stop Go." Ty knows why this is the case -- "we have good social skills," he says. Suzie asks him how he thinks things are going with the other team. His lips say "the same," but his eye roll tells you he thinks otherwise.

In this case, the eyes have it. In the other room, J.D. and Marty are arguing. J.D. has heard what Marty and Jordis have come up with and is not happy. Marty calls J.D. "hard-headed" and reminds J.D. that he gave him veto power, but J.D. won't give him that control. He ends the spat with withering assessment of J.D.'s talent -- "I love the way you write; I just don't like the way you co-write." But J.D. has his own opinion. He "wouldn't go out of his way to listen to the song they wrote." And because he only wants to attach his name to something of quality, he's just going to bow out. "That's not being in a band," Jordis tells him. "We're not in a band," J.D. reminds her. "We're competing to be in a band."

The next day, the two teams perform their songs for Dave and Andrew. "Stop Go," Ty's team's effort, turns the song into bubblegum soul, with a call-and-response chorus, which Dave describes as having an "Electric Company feel." J.D. also wasn't bowled over -- he calls it a song you'd write for your parents at band camp. It's also not what Andrew expected, although he tells the Rockers that he was impressed by their harmonies; he gets the feeling they enjoyed working together.

No one gets that feeling from Marty's team. Sitting on the floor, everyone has the lyric sheet on the floor in front of them, except for J.D., who pointedly sits behind a closed book. The "unobvious" and "vague" song Jordis and Marty worked on, with the refrain "Full Speed Ahead," features a melody that pulls against the instrumental track's riff. Dave notices that J.D. is silent and asks him why. "I just didn't feel this at all," and left the group, he explains.

Andrew tells him that although it's great that he "felt the passion to do your own thing creatively," the assignment was to see how they work together. Dave continues, telling everyone that the song was not really the focus; teamwork was, so Ty's team wins. But he's curious to hear J.D.'s version.

Using the song's driving rhythm as a jumping-off point, J.D. turns out a moody road song. Dave says that J.D. has "every element required to be a great lead singer and front man." Unfortunately, he doesn't have "every element to be a great member of a band." J.D. may have missed the point of the assignment, but Dave has to admit he wrote the better song. Marty won't go that far but calls J.D.'s peeling himself from the group and focusing attention on himself "psychotically clever."

That night, the winning team enjoys dinner with INXS at the Cafe Des Artistes. MiG, who loves seeing a different side of the band, asks the question that's been on everyone's mind -- why is Garry always credited as Garry Gary Beers? It's a nickname, even his kids call him that, he explains, and it gets misspelled constantly. The evening ends with the four Rockers singing their "winning" song for a nonplussed INXS, who pronounce it "a little corny."

The next day, the songs for the upcoming performance are again posted in the billiards room. But there's a twist. Instead of sheet music, eight envelopes are tacked to the board, one for each Rocker. For suspense, each Rocker takes an envelope at random, and reads the song title before revealing the name on the envelope. MiG gets "Baby I Love Your Way," a song he initially sneers at. But there's also a note from INXS enclosed. They want him to sing the Peter Frampton hit because he's explored his vocal range the least, and it's time for him to sing a pretty song.

Suzie discovers she's singing Sam Cooke's classic "Bring It On Home To Me," a song she's never heard. Marty's heard his song, but that's no help. Getting Britney Spears' debut "... Baby One More Time," makes him scream. INXS wants him to perform a song that's not so serious but with the caveat that it's "not as simple as it seems." Marty has no idea what he's going to do with it and enters the rehearsal room with "less confidence than he's ever had."

Will Marty, Suzie and MiG find a way into their tunes? And how will the Rockers deal with tomorrow's acoustic challenge? Tune in to CBS Tuesday at 10PM (ET/PT) to find out.