Halloween breaks out on “Ugly Betty” (7 p.m., ABC). How will we be able to tell? Not since “Batman” has a show depended so much on costume to indicate the good guys and the bad guys. And like “Batman,” “Betty” has all the subtlety of a comic book.

Our heroine’s choice of tourist poncho as fashion statement is one thing, but the brittle and arch behavior of her tormentors at the Mode magazine office is less credible. Sometimes she appears to be working in Willy Wonka’s chocolate factory.

In tonight’s holiday episode, Betty’s mean-spirited colleagues invite her to a Halloween-costume contest but neglect to tell her that she’s the only participant. Look for Judith Light in a guest role as Walter’s mother, holed up in rehab.

It’s difficult to argue with the success of “Betty” or challenge its obvious Cinderella and Ugly Duckling fairy tale appeal. Both “Working Girl” and “Pretty Woman” had similar storylines about uncertain maids catching their Prince Charmings and making remarkable fashion transformations along the way. But while they were hit movies that hold up well in eternal TV reruns, both were only two hours long. One wonders how long “Betty” can last. You can stay over-the-top only so long before you come crashing down to earth. On the other hand, “The Nanny” maintained a ludicrous romantic tension between a handsome prince and a scullery maid for almost a decade.

¢ If I have to root for a fashion-challenged female employee navigating romance in a freakish work environment, it’s going to be for Pam (Jenna Fischer) on “The Office” (7:30 p.m., NBC). Fischer’s performance and her dowdy wardrobe are utterly believable and pitch perfect. Pam dresses down to keep the goons at the water cooler from staring at her, but her frumpy layered look also expresses her hesitant personality and fear of taking chances. You know if she ever takes up with Jim (John Krasinski), they’ll both be dressing a whole lot snappier.

¢ “Decoding the Past” features “In Search of the Real Frankenstein” (8 p.m., History), which recalls the macabre experiments of 18th-century Italian scientists who tried to shock dead animals and executed prisoners back to life.

Tonight’s other highlights

¢ A surprise over a surprise on “My Name is Earl” (7 p.m., NBC).

¢ The Cardinals host the Tigers in game 5 of the World Series (7 p.m., Fox).

¢ Friends, neighbors and TV personalities chip in to rebuild a home in New Orleans on “To the Rescue: Katrina Rebuild” (7 p.m., DIY).

¢ Competitive gluttony can be a killer on “CSI” (8 p.m., CBS).

¢ On two episodes of “Grey’s Anatomy” (ABC), Izzie needs consolation (8 p.m.), the staff rallies to her support (9 p.m.).

¢ After an exonerated client kills again, a slick defense attorney (James Woods) has a moral crisis and becomes a slick prosecutor on the pilot episode of “Shark” (9 p.m., CBS).

¢ A shootout breaks out in the emergency room on “ER” (9 p.m., NBC).