Young adult fantasy adaptation The Mortal Instruments has weathered the twin storms of development hell and turnaround and is back on track with Harald Zwart calling the shots. Now the film is bulking up the cast, with Lena Headey and the freshly Emmy-nominated Jared Harris signing on.

Lily Collins plays the heroine, Clary Fray, a young woman who discovers that she’s a descendant of a line of Shadowhunters, a secret group of half-angel warriors who protect the world from demons. In the first book, City Of Bones (which will form the backbone of the first film), Fray’s mother disappears and the girl joins forces with other Shadowhunters who show her the alternate New York called Downworld that is just brimming with nasty supernatural creatures. Jamie Campbell Bower, meanwhile, will be Jace, the mysterious warrior lad she falls for.

Headey is playing Clary’s mother, Jocelyn, while Jared Harris will be Hodge Starkweather, Jace's tutor. Also jumping aboard are Godfrey Gao, Robert Sheehan, Jemima West, Kevin Durand and Robert Maillet.

Zwart will start the cameras cranking on the movie, based on Cassandra Clay’s novel series, this August in Toronto.