TONIGHT'S MUST-SEE

"American Masters: Pete Seeger: The Power of Song," 9 p.m., PBS. Pete Seeger was a city kid who discovered the music and the moods of the country. It became his life. He mastered folk music, then added to it with his own songwriting. He lived the folk life; at 88, he still splits logs for firewood. Mixed in are his politics — communism briefly, then general left-wing. He was blacklisted from TV, censored when he returned. This is a rich life — low-key one moment and high-profile the next. This documentary follows Seeger and adds comments from Bruce Springsteen, Bob Dylan and more.

OF NOTE

"Men in Trees," 9 p.m., ABC. This above-average show is in its fifth time slot, the one that could stick. "Men" has 11 new hours, mostly facing reruns. Tonight, Marin doesn't realize Jack is lost at sea. Also, she finds Cash's secret; soon, everyone in town knows it.

"American Idol," 7 p.m., Fox. The 10 remaining women perform. Last week, they had a strong outing; interestingly, the women offered harder rocking than the guys.

"Law & Order: Criminal Intent," 8 p.m., NBC. A writer goes to bed with a blonde and a brunette. When he wakes up, the blonde is dead, the brunette is missing and he's a murder suspect.

"Back to You," 8:30 p.m., Fox. Kelly (Patricia Heaton) dates a younger, competing anchor, making Chuck (Kelsey Grammer) jealous. Meanwhile, Gary covers a convention for people who dress as animal characters. And Marsh gropes for a new sign-off line.

"In Treatment," 7:30 p.m., HBO. In last week's episode, Sophie the teen gymnast gulped pills in her therapist's bathroom. Now she's back, angry that her mother has come with. The early minutes bring some crackling putdowns, followed by quietly moving moments.

"Law & Order," 9 p.m., NBC. A drunken teen catches a cab. Later, her body is found; suspects include a pimp and a prostitute.

"CSI: NY," 9 p.m., CBS. A mass murder occurs at the "Amityville Horror" house in Long Island.