"Game of Thrones" actress Lena Headey and "Mad Men" actor Jared Harris have joined the cast of "The Mortal Instruments: City of Bones," according to The Hollywood Reporter.

Screen Gems is spearheading the adaption of Cassandra Clare's bestselling book series with Constantin Film and Unique Features backing the project, which will lens in Toronto in August for an Aug. 23, 2013 release.

"City of Bones" centers on 15-year-old Clary Fray (Lily Collins), a seemingly ordinary girl who discovers she is the descendant of a warrior clan called Shadowhunters, who combat demons around the world.

In addition to Headey and Harris, Canadian actor Godfrey Gao ("All About Women") is also joining the production.

Headey ("300") plays queen Cersei Lannister on HBO's acclaimed fantasy series. In September, she appears in "Dredd 3D." Harris will appear in Steven Spielberg’s "Lincoln" as Ulysses S. Grant; the film opens in December.

Harald Zwart ("The Karate Kid") is directing "City of Bones" from a script by Jessica Postigo and I. Marlene King. Martin Moszkowicz and Dylan Sellers will executive produce, with Robert Kulzer, Michael Lynne and Robert Shaye in producer roles.

"The Mortal Instruments" also stars Jemima West ("The Borgias"), Jaime Campbell Bower ("The Twilight Saga: Breaking Dawn - Part 2"), Kevin Durand ("I Am Number Four," "Real Steel") and Robert Maillet ("Sherlock Holmes," "Immortals").

"City of Bones" ranked No. 8 in children's books on the New York Times Best Seller list in 2007.

Should the book's adaption enjoy box office success, audiences can expect to see big screen treatments for the series' other installments, which include "City of Ashes," "City of Glass," "City of Fallen Angels" and "City of Lost Souls."

The next book in the series, "City of Heavenly Fire," is expected to conclude the storyline.