TONIGHT'S MUST-SEE

"American Idol," 7 p.m., Fox; and "Nashville Star" debut, 10 p.m., USA Network. For fans of competition reality shows this is a big night, with three straight hours. First comes "Idol," which has finally trimmed to 12 finalists. They all perform tonight. Then comes "Nashville Star," which begins with only 10. This time, Cowboy Troy — who mixes rap and country into a fun package — hosts with Wynonna. Troy's pals Big & Rich will perform and will be guest judges with Phil Vassar and Anastasia Brown. The three youngest people are 20; the oldest, Nicole Jamrose, is 33, a mother of two. Three are originally from California, two from Indiana, the rest from the South. The lineup includes a former Navy guy who did two tours in the Persian Gulf, a former Miss Albuquerque and someone who says she quit corporate life to become "a female Travis Tritt."

OF NOTE

"NCIS," 7 p.m., CBS. The son of a military officer is holding his class hostage.

"Joey," 7 and 7:30 p.m., NBC. Joey's first movie is about to debut. He's upset because Carmen Electra has a bigger billboard — and because his father's interests are clearly different from his. That's followed by a rerun in which a former girlfriend has an embarrassing tape.

"Scrubs," 8 and 8:30 p.m., NBC. J.D. is increasingly bitter about Keith the too-perfect intern. Others are fuming, too, now that people know about Keith's romance with Elliot. That's followed by a rerun that imagines the doctors in a traditional situation comedy with a studio audience.

"The Unit," 8 p.m., CBS. Questions are being raised about a rescue operation in Idaho. Meanwhile, Jonas' team tries to recover a fallen Chinese satellite.

"The Shield," 8 p.m., FX. Setting up next week's season finale, Lem is ready to plead guilty to heroin possession. Worried about how Lem would survive inside prison, Vic is willing to cut a deal with his old enemy Antwon (Anthony Anderson). There are more troubles ahead, including a crisis in the long friendship between Dutch and Claudette.

"Boston Legal," 9 p.m., ABC. Alan defends his secretary, charged with tax evasion. Meanwhile, Paul decides something must be done about his daughter's drug use.

"Law & Order: Special Victims Unit," 9 p.m., NBC. Cody Kasch (Zach on "Desperate Housewives") and Marcia Gay Harden play suspects in this rerun, which involves a school shooting.

TONIGHT ON KHNL NEWS 8

Tonight on KHNL News 8, Walter Makaula profiles Hawaii's Most Wanted. Will your tip bring another crook to justice? Tune in at 6 and 10 p.m.