'Castle' Season 6 Sneak Peek: Castle And Beckett Are Back Together In 'Need To Know' (EXCLUSIVE VIDEO)

In the Oct. 7 episode of ABC's "Castle" (Mondays at 10 p.m. ET), now in Season 6, Castle (Nathan Fillion) manages to insert himself into the investigation into the murder of former child star Charlie Reynolds -- who rose to fame playing the lovable nerd on an early '90s high school sitcom -- even while Beckett (Stana Katic) is in D.C. with the FBI.

As you'll see in HuffPost TV's exclusive clip above, Gates (Penny Johnson Jerald) is less than thrilled about Castle's involvement in the case, but the precinct soon has bigger fish to fry when Agents Beckett and McCord (Lisa Edelstein) arrive from Washington to take over the investigation, creating competitive tension in the 12th. But why would a washed-up actor's death warrant Federal scrutiny? Whatever the reason, Beckett and McCord aren't telling. Elsewhere in the episode, Castle has to contend with a new face at the 12th, NYPD Detective Frank "Sully" Sullivan (Joshua Bitton) and Antonio Sabato, Jr. guest stars as Ramon Russo, the victim's former sitcom costar.

Check out Castle and Beckett's unexpected (and surprisingly awkward) reunion above, then hit the comments to share your predictions for the episode, titled "Need to Know."

Castle Season 5