This show returns with fresh episodes just as Serena returns from her adventure in Spain. Also back on the scene: Nate's wealthy grandfather, who makes a secret pact with Blair. And while it may be too late for the rest of us to celebrate Passover, it's not too late in the Waldorfs' world, so they host a Seder for their newest family members. Among the catering staff: a displeased Dan, who didn't realize he'd be serving his friends when he got a job to earn money for college.
* Bones (8 pm/ET Fox)
Boneheads, rejoice! This week we get two episodes of the series: one tonight, and another at its regularly scheduled time on Thursday (8 pm/ET). The first one focuses on the loss of a colleague from another department at the Jeffersonian, though Brennan is skeptical of the official cause of death. Later in the week, Booth helps a friend and fellow law-enforcement officer from Japan when the guy's sister goes missing in Washington, D.C.
* Dancing with the Stars (8 pm/ET ABC)
It's time for an event that has proved to be one of the highlights of past seasons: the group dance! This round, that number will have a 1960s theme, so it's sure to be groovy. And for a new fun twist, the contestants got to design this week's costumes for their regular performances. We got some hints at what this may look like last week, as LT promised that Edyta would be more "covered up," Shawn was looking into leotards, and Ty was suggesting the use of denim.
* Chuck (8 pm/ET NBC)
A vogue agent turns rogue agent tonight. Chic superspy Sarah defies government protocol and operates outside the rules - for Chuck's sake. Here, Sarah and Chuck take a quantum leap, going AWOL in a stealthy quest to rescue Chuck's father (Scott Bakula) from Fulcrum forces. They'll go undercover and possibly under the covers, as they inch closer to one another while free from the governmental surveillance that usually eyes them. Meanwhile, the grunting and perpetually mirthless Casey works to pinpoint their secret location. There's more at Buy More: Morgan turns into a Nerd Herd outcast after unwittingly getting snooty Emmett promoted. Chevy Chase guest stars.
* Medium (10:01 pm/ET NBC)
Allison takes a stalk on the wild side in Part 1 of a two-parter. Allison always has a vision quest, but tonight her visions turn especially nightmarish when they center on her stalker: Lucas Harvey, a twisted zealot who's devoted to ending Allison's paranormal work for good. Allison's chilling dreams then come to life when Harvey makes an actual appearance, putting Allison and her family in grave danger. Meanwhile, Joe struggles over crucial decisions that could save his company. The conclusion airs next week.