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.

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Needless to say, babysitting gives the newly engaged couple a chance to play house. But based on the exclusive sneak peek below, the results might be mixed. Although Castle proudly proclaims, "I don't know if you know this about me, but babies love me. I'm the Baby Whisperer," Beckett has a different reaction."I'm suddenly getting a clear and frightening visual as to what my future will look like," Beckett says. Might she be fearful of raising a child of her own?Also feeling the pressure is Detective Ryan (Seamus Dever

), who, despite training for the arrival of his own baby, isn't able to get little Cosmo to stop crying. Yes, that's right: Castle has named the baby Cosmo. To find out why, click play below.Castle airs Mondays at 10/9c on ABC.

Castle sneak peek: Can Castle and Beckett handle… a baby?

Exclusive sneak peek from Castle