When a construction crew digs up the body of an infamous mobster last seen in the 1970s, the team at the 12th precinct finds itself trying to solve a murder over three decades old on Castle Season 6 Episode 20.
But when the only possible witness lives with the delusion that it's still 1970-something, Castle, Beckett and the gang go all in to play into his reality in the hopes of catching the killer.
Check out these totally groovy outfits and far out hairstyles in these photos from "That '70s Show."
Also, don't forget that when you need your fix, you can always watch Castle online here at TV Fanatic.
C. Orlando is a TV Fanatic Staff Writer. Follow her on Twitter.