Variety reported Wilkes will appear in the mysterious, titular town just as a feud between rival families escalates.
Kathy Bates won the Best Actress Oscar for playing Wilkes, an obsessed fan who kidnaps and tortures her favorite author, in the 1990 film adaptation of Misery. Laurie Metcalf also portrayed Wilkes in a Broadway staging of Misery in 2015.
Caplan is best known for her work in Mean Girls, Cloverfield, Masters of Sex and 127 Hours.
Castle Rock is set in King's supernatural universe and pulls together characters and locations from his canon to create new stories.