Mixing it up tonight - with four contestants left - to decide who makes the semi-finals the idol hopefuls will sing twice. Once on their own and once in duet. And after a freak accident on stage before dress rehearsal, where one of the towers collapsed minutes before recording started, the contestants will hit the stage with their raw live performances, having had no chance to rehearse.

For the first time ever on American Idol, a Led Zeppelin number will be performed as Adam Lambert covers Whole Lotta Love.

17-year-old Allison Iraheta will perform Janis Joplin's Cry Baby, Kris Allen's solo is Come Together by The Beatles, while Danny Gokey will try out his pipes on Aerosmith's Dream On.

For the duets, Kris teams up with Danny for a version of Styx's Renegade while remaining two Allison and Adam sing Slow Ride by Foghat.

Friday night's results show will include a performance from Paula Abdul - the first time she has ever performed on Idol - who will showcase her new single "I'm Just (Here for the Music)."