TONIGHT'S MUST-SEE

"Big Bang Theory," 7:30 p.m., CBS. This comedy has quickly found its touch and tonight's episode sounds promising. Leonard and Sheldon, the likable nerds, have been invited to a party put on by their hot neighbor, Penny.

OF NOTE

"Chuck," 7 p.m., NBC. Chuck meets a gadget geek who would like to escape the CIA's grasp; that spurs divided loyalties. Meanwhile, Morgan reminds Chuck that Halloween is supposed to be their big day.

"How I Met Your Mother," 7 p.m., CBS. Despite his hopes of saving the world, Marshall takes a job with a slick lawyer.

"Heroes," 8 p.m., NBC. Claire really doesn't get the idea of maintaining a low profile at her new school. Tonight she's nudged into retaliating against the head cheerleader. Meanwhile, Saresh has an ethical dilemma with The Company, Peter enters a mysterious doorway, Sylar seems to have evil intentions toward Maya, and Hiro really wishes he could be the one the princess loves.

"Two and a Half Men," 8 p.m., CBS. Jake sneaks off to a concert after his dad told him not to.

"Samantha Who?" 8:30 p.m., ABC. Samantha is still learning just how disliked she had become before her amnesia. She goes to a wedding but finds the bride has rescinded her invitation.

"The Bachelor," 9 p.m., ABC. Brad visits the homes of the final four women. Then one of them is ousted.