NGTV Guide: Monday, May 11

We get a double-dose of prom tonight, plus insight into the pasts of a couple of leading ladies. Gotta love May sweeps!

Gossip Girl – the CW 8/7c
“Valley Girl” – In this backdoor pilot for a spinoff, Lily flashes back to her own high school days in the ’80s when she’d been thrown out of a boarding school and sent home to Los Angeles. No Doubt guests as an ’80s band, which in and of itself is enough to tune in, plus we see Nate & Blair’s not quite perfect prom.

Castle – ABC 10/9c
“A Death in the Family” – The season finale revolves around the murder of a plastic surgeon, but the real meat of the episode comes as Alexis goes to her first prom and Castle discovers something very unsettling about Beckett’s past. We’re betting it’s not that she was thrown out of boarding school.