Castle makes a groovy return tonight when Castle (Nathan Fillion) and Beckett (Stana Katic) take on a quirky case involving the newly discovered body of a missing mobster who was murdered in 1978.

The Castle crew has to pretend it is 1978 in a fun episode. ... Castle: That ’70s Show review. ... While we are a little unsure of just when Harold stopped pretending it was 1978 I am not sure.

Castle Becomes That '70s Show For a Night. Castle makes a groovy return tonight when ... "He's excited that [this ruse] is taking his mother's focus off their wedding for a little while," Katic says.