Dylan McDermott is going from horror on the small screen to horror on the big screen.

The American Horror Story actor has joined the cast of Mercy, an adaptation of a Stephen King story being produced by Blumhouse and Wonderland Sound and Vision.

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Universal is distributing.

Peter Cornwell is directing the horror thriller, which revolves around two brothers (Chandler Riggs and Joel Courtney) who go with their mother (Frances O’Connor) to take care of their grandma. Unbeknownst to them, the grandmother is a witch who made an evil deal using black magic years earlier.

McDermott will play a man who long ago had a relationship with the mother and still has feelings for her, even though he is now married. 

Mercy is based on King’s short story Gramma, which was first published in Weirdbook magazine in 1984.

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Jason Blum and Wonderland's McG and Mary Viola are producing. Matt Greenberg wrote the script.

McDermott, who appeared in the well-regarded indie The Perks of Being a Wallflower, plays a key role on FX’s American Horror Story: Asylum after starring in the show's first season.

He is repped by CAA, The Schiff Co. and Hansen, Jacobson.