Nathan Fillion Nathan Fillion

Richard Castle will have an unexpected guest at Thanksgiving this year.

On Monday's Castle (10/9c, ABC), Beckett (Stana Katic) and Castle (Nathan Fillion) must care for a baby boy after a dying man leaves the child with a priest. While trying to solve the murder, the pair also takes on the difficult task of finding the orphan's parents.

Castle postmortem: Stana Katic on "crushing" twist and Beckett's next move