Sean is scheduled to guest star on the second half of the fifth season of Monk, USA Network’s popular obsessive-compulsive detective show. According to USA’s official site, he’ll be in the episode titled “Mr. Monk is at Your Service.” Here’s the synopsis:

When Natalie suspects foul play in the deaths of her parents’ wealthy neighbors, Monk goes undercover as a butler to investigate. Sean Astin and Holland Taylor guest star. Premiere date is TBD.

Hmmm, sounds like he might be playing a baddie! The new season premieres in January 2007.