Here's a look at tonight's sci-fi TV:
Fringe, 'Olivia. In the Lab. With the Revolver' – Olivia struggles not to reveal what she learned about Peter during last week's awesome '80s flashback hour. Meanwhile, the team deals with a very creepy threat: a from of cancer that spreads and kills by touch. (9 p.m. ET on Fox)
FlashForward, 'Queen Sacrifice' – Mark leaves his family behind in order to protect them. Later, he and Vogel seek out the FBI mole. Elsewhere, Olivia finally discovers who sent that cryptic text message about Mark's drinking. (8 p.m. ET on ABC)
The Vampire Diaries, 'Let the Right One In' – Yep, that's the episode title! Pretty cheeky, huh? ... The tomb vamps abduct Stefan, and the boys meet a dangerous new enemy. Caroline makes a shocking discovery that rocks Mystic Falls. (8 p.m. ET on The CW)
Supernatural, '99 Problems' – The brothers face a town full of people preparing for the Apocalypse and a mysterious preacher's daughter who claims to be a prophet. (9 p.m. ET on The CW)
Head after the jump for clips and more TV picks.