TONIGHT'S MUST-SEE

"The New Adventures of Old Christine," 7:30 p.m., CBS, and "The Real Wedding Crashers" debut, 9 p.m., NBC. Weddings offer an unending pool of comedy. Expectations are high; there's a wonderful potential for failure. "Christine" mines that perfectly. Its hero (Julia Louis-Dreyfus) is full of flaws; bump her against a distrustful bride and you have sharp humor. "Real Wedding Crashers" has mixed success. It's a candid-camera show in which the bride and groom are in on the gag. Some of the regulars are great at dry humor. There's great work from Steve Byrne as a distracted minister and Desi Lydic as a spaced site manager. Some others overplay their roles. The gags are funny but lack a sharp finish.

"Heroes" return, 8 p.m., NBC. As the first season resumes, this show keeps getting deeper and darker. Tonight's hour is compelling but a tough ride. It has handed its villains too much power. One is an invincible killer; another can instantly take the form of other people. Gradually, the "heroes" learn who's related and why. They also get a chilling overview from Linderman, who sees even darker days ahead.

OF NOTE

"Cities of the Underworld" debut, 6 p.m., History Channel. There is a lot of history beneath older cities, this series says. It starts with Edinburgh, Scotland, where there were body snatchers, dungeons and walled-in, underground neighborhoods.

"Dancing With the Stars," 7 p.m., ABC. Last week, Clyde Drexler became the first male celebrity ousted. Five men and two women remain.

"Diners, Drive-Ins and Dives," 7 p.m., Food Channel. In the midst of what looks like a Texas wasteland, there's an old shack. Emerging from there, said host Guy Fieri, is delicious food, with 140 customers on a weekend night. We view several such shabby-looking spots that obsess on food.

"Two and a Half Men," 8 p.m., CBS. Alan befriends a gay man and his daughter. Jake soon falls for the girl; she's played by Kay Panabaker, 16, whose sister Danielle co-stars on "Shark."

"American Experience: Summer of Love," 9 p.m., PBS. Given 40 years of perspective, this is a wonderfully balanced portrait of the summer of 1967 in San Francisco. We hear people nowadays (including actor Peter Coyote) discussing their idealism at the time. We also hear what went wrong when too many newcomers arrived.

"King of Queens," 8:30 p.m., CBS. Adam Sandler guests as Doug's high school pal. He's the vice principal now, but at the class reunion, he agrees to aid a revenge scheme against the mean-spirited principal.