ABC preempted last week’s episodes of “Happy Endings” (ABC at 8, 8:30 p.m.) to cover news about the hunt for a suspect in the Boston Marathon bombing, so the network is airing them now and pushing the season finale to next week. Penny hooks up with Jane’s boss as a way to get over her broken engagement, and later, Max’s scorned roommate — guest star Mark-Paul Gosselaar — is back to ruin Max’s life . . . until he realizes that Max’s life is so sad there’s nothing worth ruining.

The boss of Retro Fitness, which has branches in Maryland and Virginia, goes on “Undercover Boss” (CBS at 8) to find out what’s really happening at the company.

Sheriff Lamb and Jack team up to find out what happened in the murder of a craps dealer on “Vegas” (CBS at 9), which results in Mia getting taken hostage by a suspect in the case. Meanwhile, Savino has some nefarious plans for when the Tumbleweed Casino reopens.

“Grimm” (NBC at 9) also was preempted last Friday, so it airs this week. And remember, starting next week, the show moves to Tuesdays for the rest of the season. In this episode, Juliette seeks help dealing with memories of Nick, while a volcano threatens to cover the city in lava.

Martin decides to bite the bullet and tell his complicated story to the authorities, but he has trouble getting a detective to believe him, let alone help him, on “Touch” (Fox at 9).

A man who wakes up in a park covered in his girlfriend’s blood insists he has no idea what happened the night before on “Blue Bloods” (CBS at 10), and Danny doesn’t believe him until test results show the man took a strong narcotic.

One bride-to-be’s dress was ruined in Hurricane Sandy, so she goes to look for a replacement on “I Found the Gown” (TLC at 10), while another woman wants a “runway look” for the big day.

Singer Christina Milian joins the panel on “Fashion Police” (E! at 10) for a snarky half-hour of judging celeb outfits.

Actor Jon Hamm, magician Ricky Jay and musical guests the So So Glos are on “Late Show With David Letterman” (CBS at 11:35).

“The Tonight Show With Jay Leno” (NBC at 11:35) hosts actor Robert Downey Jr. and singer Avril Lavigne.

— Emily Yahr