TONIGHT'S MUST-SEE

"American Idol," 7 p.m., Fox. This is country-music night on "Idol." That has killed some top talents, including Mandisa last year. This year might turn out fine, though: The mentor is Martina McBride, one of the great singers of powerhouse ballads. "I'm really looking forward to seeing it," said Kellie Pickler, who sang McBride songs last year. "I've always been a big Martina fan." All three big-voice divas — Melinda Doolittle, LaKisha Jones and Jordin Sparks — could soar. Last week, the intricacies of Latino music seemed to overwhelm many of the singers; Haley Scarnato was ousted and now there are seven survivors.

OF NOTE

"Dave" (1993), 6 p.m., Hallmark Channel. This clever comedy has Kevin Kline as an ordinary chap who is asked to impersonate the president. The first lady, Sigourney Weaver, goes along with it.

"The Shield," 7 p.m., FX. After two superb episodes, culminating with the arrest of Kavenaugh for tampering with evidence, this is a sharp drop in quality. Mackey is obsessed with his belief that Guardo killed Lem. Shane (the real killer) can't stop him. "The Shield" has painted itself in a corner with nowhere to go for now.

"George Lopez," 7 and 7:30 p.m., and "Dancing With the Stars," 8 p.m., all ABC. The second "Lopez" episode may appeal to "Dancing With the Stars" fans. Mario Lopez, the show's runner-up this fall, plays George's old friend, now falling for his niece. Afterward, "Dancing" dismisses its fourth star.

"Nova: The First Flower," 8 p.m., PBS. Scientists search a Chinese mountain range, for signs of the planet's first flowers. You won't get any definitive answers here, but you'll see some gorgeous pictures on the way.

"House," 8 p.m., Fox. A 6-year-old girl seems to be aging at a ferocious speed. The same might be happening to her 8-year-old brother, who is hitting on Cameron.

"Law & Order: Criminal Intent," 8 p.m., NBC. A soldier disappears while on leave, in this rerun. She's the daughter of a police commissioner and his wife (Michael Biehn and Fran Drescher); Goren, already worried about his mother (Rita Moreno), is called back from Thanksgiving vacation.

"Boston Legal," 9 p.m., ABC. Alan Shore works on the case of a woman suing a department store for selling "pornographic" dolls to kids. Meanwhile, Denny Crane is in trouble, after his politically incorrect comment to a job applicant.