When the body Vince Bianchi, a mobster killed in 1978 is discovered, Castle Season 6 Episode 20 steps back in time to find the killer.

Vince's best friend, Harold has delusions of it still being 1978, so with Martha's help the 12th precinct is transformed into "That '70s Show" to help jog his memory about the night Vince disappeared. 

Little did Castle and Beckett realize that Vince and Harold were more than friends, and Vince was killed by Maria when he decided he couldn't marry her and bring the two mob families together. 

If you can't get enough of this groovy episode, you can always watch Castle online right here at TV Fanatic. Can you dig it?

Watch Castle Season 6 Episode 20 Online

C. Orlando was a TV Fanatic Staff Writer. Follow her on Twitter.