8 p.m., FOXHugh Laurie, the team spends time together reminiscing about the past when the hospital goes on lockdown.
Season 1 finale, 8 p.m., CWBritt Robertson) makes a big announcement, and recently-engaged Cate (Shiri Appleby) stresses about her feelings for Baze (Kristoffer Polaha) and Ryan (Kerr Smith).
9:30 p.m., CBSJim Parsons) to a bowling match. Plus, a fight between Leonard (Johnny Galecki) and Penny (Kaley Cuoco) threatens their relationship.
10 p.m., ABCNathan Fillion) and Beckett (Stana Katic) investigate the death of late-night talk-show host Bobby Mann (guest star Tom Bergeron). Plus, Fred Willard appears as Mann's sidekick and Kelly Carlson guest-stars as a starlet with eyes for Castle. Did somebody say "love triangle"?
11 p.m., COMEDYBreaking Bad star Bryan Cranston.
Also on the airwaves...
Dancing with the Stars, 8 p.m., ABC
How I Met Your Mother, 8 p.m., CBS
10 Things I Hate About You, 8 p.m., ABC Family
Rules of Engagement, 8:30 p.m., CBS
Two and a Half Men, 9 p.m., CBS
24, 8 p.m., FOX
Trauma, 9 p.m., NBC
Gossip Girl, 9 p.m., CW
Intervention, 9 p.m., A&E;
CSI: Miami, 10 p.m., CBS
Damages, 10 p.m., FX
Nurse Jackie, 10 p.m., SHO
Saving Grace, 10 p.m., TNT
Anthony Bourdain: No Reservations, 10 p.m., TRAVEL
United States of Tara, 10:30 p.m., SHO
MLB Baseball: Red Sox v. Twins, Brewers v. Cubs
What are you watching tonight?
Follow TV.com writer Stefanie Lee on Twitter: @StefAtTVDotCom