Based on Mitch Cullin's novel of the same name, the screenplay is written by playwright Jeffrey Hatcher ( Tuesdays with Morrie, Never Gonna Dance).
Linney ( Time Stands Still, Sight Unseen) will portray housekeeper Mrs. Munro, with A Doll's House star Morahan also added to the cast.
Set in 1947, the flim follows the retired detective, who is haunted by an unsolved case from 50 years ago. Living in a small Sussex village with his housekeeper and son, who also solves crimes, Holmes can only remember fragments of the case.
The film is the second collaboration between director Condon and McKellen, who also worked together on "Gods and Monsters." Filming will begin this summer.