Dermot Mulroney To Star In Insidious: Chapter 3 The new family set to be terrorized in Blumhouse threequel Insidious: Chapter 3 has added Dermot Mulroney, according to writer/first time director Leigh Whannell via Twitter today: HUGELY excited to officially announce that great actor/great human Dermot Mulroney has been cast as one of the leads in Insidious Chapter 3! — Leigh Whannell (@LWhannell) June 25, 2014 Whannell is taking over for James Wan in the director’s chair, while Mulroney is one of the actors who will be taking the franchise on a new journey without original leads Patrick Wilson and Rose Byrne.