We've got two movies for the price of one here. In the incident-packed first half we have New York teen Clary (Collins, Mirror Mirror) chased around the city by bad guys and dogs that change into scary looking demons because they believe Clary is in possession of 'the cup', a mortal instrument that does mad stuff altogether. Of course, Clary has absolutely no clue about it, or what is going on in general, or if this new dimension, one that has just revealed itself to her, is actually real. She needs handsome best friend Simon (Sheehan) and handsome shadow-hunter Jace (Campbell Bower) to help her through the mess.
Director Harald Zwart (One Night At McCool's, The Karate Kid) throws everything into the mix at a breakneck pace, stopping only occasionally to bring Clary, and the audience, up to speed. There's a welcome level of threat and violence that Harry Potter and Twilight, two movies Mortal Instruments tries to ape, didn't have. What's more, unlike Twilight's Bella who feels like a mopey bystander for most of Twilight's running time, Collins is forced to get stuck in from the off. It's exciting stuff.
But then something happens and everything just gets laughable. The second half might be busy too but where the audience was once asked to get their heads around the pacy action and chunky exposition, now they're asked to go along with embarrassing plot twists and revelations, puzzling uses of music, clichéd love triangles and some questionable acting; Robert Sheehan and Aidan Turner more than hold their own amongst the Hollywood types, however. It's as if the second half was hijacked by those determined to scuttle their own film with a naffness that knows no bounds. The story gets far too familiar for its own good - if you thought Oblivion cherry-picked from seven or eight sci-fi movies, this does the same with other teen fantasy movies. Its only hope is that the woeful plot developments turn the movie into a campy cult classic.
There's just enough here to say roll on City of Ashes, though. We could do with a laugh.