TONIGHT'S MUST-SEE

"Scrubs," 8 p.m., NBC. This isn't your usual medical condition: Patti (Stephanie D'Abruzzo) says people at the hospital are singing — not talking — to her. And, oddly enough, she's singing back. We promptly sympathize with her, because ... well, we hear the singing, too. What follows is one of the freshest delights in a long time — for one episode, a situation comedy morphs into a full-scale musical. The songs are mainly by Robert Lopez and Jeff Marx, the Tony-winning composers of "Avenue Q"; Deb Fordham (who wrote the witty script) and Paul Perry join them for some of the lyrics. These are clever songs, well executed. The result is a delight.

OF NOTE

"CSI: Crime Scene Investigation," 7 and 8 p.m., CBS. First is a rerun in which the mother at a wedding has been killed and tied to the back of the couple's car. Then a new episode: With Grissom gone on leave, a day-shift worker (Liev Schreiber) helps on a case. A runaway's body has been found behind a hotel; this may be the work of a serial killer.

"Ugly Betty," 7 p.m., ABC. Betty tries to help her boss snap out of his funk. Meanwhile, scheming Wilhelmina prepares to take over.

"My Name is Earl," 7 p.m., NBC. Earl finds that it's hard to make amends with a dead guy. Meanwhile, Randy and Catalina must make their marriage seem legitimate; they're looking for an apartment.

"The Office," 7:30 p.m., NBC. Oscar Nunez, who plays Oscar (appropriately) on the show, has been gone lately. He was making a new comedy ("Halfway Home") that debuts March 14 on Comedy Central. He returns to the show tonight and we're told that Oscar is back from a long vacation, with mixed feelings about being back.

"Grey's Anatomy," 8 p.m., ABC. George's dad hovers near death and Meredith's sister's baby has barely survived. Meanwhile, a teen (the gifted Mae Whitman) with a severely curved spine has learned that the insurance company won't pay for experimental surgery.

"30 Rock," 8:30 p.m., NBC. It's "bottoms-up day," so Jack (Alec Baldwin) is a page and Kenneth the Page is a manager. Also, Liz is shocked to be attracted to a guy known mainly for his great hair.

"ER," 9 p.m., NBC. This reruns the episode that had Gates — then still a paramedic — helping Neela get home. Also, Abby's mom (Sally Field) tries to soothe her daughter's grief.

"Shark," 9 p.m., CBS. The only survivor of a serial killer is too frightened to testify.

"Men in Trees," 9 p.m., ABC. Marin has writer's block, just as her editor comes to visit.

"Nashville Star,"10 p.m., USA Network. Miranda Lambert — who finished third during the first season, then surpassed everyone else in record sales — performs.