TONIGHT'S MUST-SEE

"Nashville Star," 8 p.m., NBC. A week before the finale, this hour determines the winner. Viewers will learn which of four finalists was voted out. Then, they'll have a last chance to vote for the top three. The lineup includes three Texans and lots of variety. Gabe Garcia, 28, has a strong voice; Coffey (that's his stage name), 29, doesn't, but he's a big, handsome, single dad. Melissa Lawson, 31, has five sons and a powerhouse voice. The dark-horse prospect is Shawn Mayer, 21, from small-town Iowa. Since switching mentors (from Jeffrey Steele to Jeffrey Steele), she's been singing with simmering passion.

OF NOTE

"Big Bang Theory," 7 p.m., CBS. In a terrific rerun, the four friends combine to buy an ultimate prize for any science-fiction fan — the time machine from a classic movie. Then real-life complications begin.

"High School Musical: Get in the Picture," 7 p.m., ABC. This wraps up the West Coast auditions. Next Sunday, survivors from both coasts meet.

"Samantha Brown: Passport to China," 9 p.m., Travel Channel. Brown ranges from a gymnastics academy to the sprawling Forbidden City. She even has an occasional tip that's quite helpful. Discouraged by the overcrowded Great Wall? Just keep walking, she says. Most people don't go far, so the crowd soon thins out.

"Air Jaws: Sharks of South Africa" (5 p.m.), "Surviving Sharks" (6) and "Day of the Shark" (7), Discovery Channel. Shark Week continues. "Surviving Sharks" is new; "Air Jaws" has some great footage.

"House," 8 p.m., Fox. Janel Moloney (Donna in "The West Wing") plays someone with a perplexing paralysis.

"Saving Grace," 7 p.m., TNT. A squad member has been killed and Grace suspects the widow (Amy Madigan).

"Secret Diary of a Call Girl," 8:30 p.m., Showtime. Ben recently learned that his friend, Belle, is a prostitute. In a so-so episode, he wants to join her when someone is hiring a man-woman duo.