Turns out she belongs, without knowing it, to an ancient supernatural breed (although she seems to be the only remaining Shadowhunter without a British accent).
These crusaders battle evil with style. When she and her crew - Jamie Campbell Bowen (young Arthur in TV's Camelot), Jemima West of The Borgias, and Gossip Girl's Kevin Zegers - head for a Satanic goth nightclub to meet the High Warlock of Brooklyn (Godfrey Gao), they look like they just stepped out of a Paramore video.
Though imaginatively directed by Harald Zwart, Mortal Instruments, which is adapted from Cassandra Clare's YA novels, is marred by significant flaws.
The best actor in the cast - Lena Headey of Game of Thrones - exits way too early. And the most riveting character - a wonderfully villainous turn for Jonathan Rhys Meyers - enters far too late.
This is ostensibly a teen romance, but all sweetness is lost in a sea of violence and gross special effects. Yet the actual battle scenes are disappointing.
The film's primary problem is its premature climax. It goes for the big action crescendo early, then tries to sustain that wild intensity for a solid hour. Admirable but exhausting.
You don't want to think too hard about the plot, because the young-love story takes a creepy incestuous turn and because Clary's powers essentially all derive from cutting.
On the surface, Mortal Instruments is a slick teen thriller. Just overbaked and unoriginal.
The Mortal Instruments: City of Bones ** (Out of four stars)
Directed by Harald Zwart. With Lily Collins, Jamie Campbell Brown, Robert Sheehan, and Lena Headey. Distributed by Screen Gems
Running time: 2 hours, 10 mins.
Parent's guide: PG-13 (intense violence, adult themes)
Playing at: area theaters
Contact David Hiltbrand at email@example.com or follow on Twitter @daveondemand_TV. Read his blog at www.inquirer.com/daveondemand