One Tree Hill (8 p.m., CW57)- Lucas begins his book tour and is joined by a familiar face. Nathan is forced to question his health when he is given an opportunity to play basketball again.

Law & Order: Criminal Intent (9 p.m., NBC10) - A charming con man targets a lonely single mother as part of his scheme to hit an armored truck carrying millions of dollars. Nichols and Wheeler investigate the case when one of the con man's partners dies weeks later in an explosion.

Gossip Girl (9 p.m., CW57) - Serena discovers that Aaron has been keeping a secret from her. Hoping it will help her get into Yale, Blair agrees to baby-sit the daughter of a prominent donor, but things soon spin out of control. Jenny and Agnes plan a guerrilla fashion show that will make or break Jenny's chances.

The Big Bang Theory (9:31 p.m., CBS3) - Leonard and Penny's first date doesn't go well, and Penny shares her frustration with a reluctant Sheldon, and a secret comes out that could nip the relationship in the bud. Sara Gilbert becomes a regular cast member, playing Leonard's gal pal Leslie Winkle.

Late Show With David Letterman (11:35 p.m., CBS3) - Hayden Panettiere; Conor Oberst and the Mystic Valley Band perform.

The Tonight Show With Conan O'Brien (11:35 p.m., NBC10) - Howie Mandel; Alanis Morissette; Death Cab for Cutie performs.

Jimmy Kimmel Live (12:06 a.m., 6ABC) - Comic Artie Lange; chef Adam Perry Lang; No Doubt performs.

The Late Late Show With Craig Ferguson (12:37 a.m., CBS3) - Eric Idle; Dr. Lisa Masterson.