TONIGHT'S MUST-SEE

"Girl, Positive," 6 p.m., Lifetime. Rachel (Andrea Bowen) is a teen at an upscale high school. Like most of her classmates, she looks great. Like many, she's sexually active. Then come revelations that have her wondering if she might be HIV-positive. An earnest teacher (Jennie Garth) wants everyone to be tested. "Girl, Positive" could have been empty. Fortunately, it has a smart script by Nancey Silvers and first-rate direction by Peter Werner, who did Lifetime's excellent "Gracie's Choice." Bowen — best known as Susan's daughter Julie in "Desperate Housewives" — is perfect. She finds just the right mixture of emotion and restraint.

"Simon Schama's Power of Art," 10 p.m., PBS. This hour traces the troubled and brilliant life of 16th-century painter Michelangelo Merisi da Caravaggio. Simon Schama writes beautifully and delivers it poorly. Still, it's an interesting story.

OF NOTE

"The Closer," 6 p.m., TNT. The body of a slain youth leads to a probe of gangs and of a priest who works with gang mothers. Also, Brenda's dad learns she's living with a guy.

"Heartland," 7 p.m., TNT. Last week's opener was well-made, but one-note. Now this promising series adds much-needed variety. It introduces a new doctor (Rockmond Dunbar of "Prison Break"); it also gives extra attention to the angry, 14-year-old daughter of Dr. Nathaniel Grant and his ex-wife Kate Armstrong, who works with the organ donors.

"The New Adventures of Old Christine," 7:30 p.m., CBS. In a rerun, Christine needs money for tuition.

"Kyle XY," 8 p.m., ABC Family. Jessi, fresh from the same lab as Kyle, has fallen into the wrong hands. Now she's trying to get close to him.

"Two and a Half Men," 8 p.m., CBS. In an acerbic (and funny) rerun, Charlie and Alan are convinced no one would mourn their mom if she died.

"History Detectives" season-opener, 9 p.m., PBS. Three artifacts are pursued, with only moderately interesting results. A 3-D screen may have been used during the Cuban missile crisis; an aluminum recording may hold a lost "Amos and Andy" radio broadcast; and a painting may have had a key role in the women's suffrage movement.

"Science of Love," 9 p.m., NBC. This special offers a man 50 possibilities. He dates his choice and the woman chosen scientifically.