Rock-dumb Hong Kong thriller That Demon Within is exhausting, and only sometimes batshit enough to be engaging. Popular action filmmaker Dante Lam (The Beast Stalker, Stool Pigeon) never capitalizes on the exciting conceit he and co-writer Wai Lun Ng have come up with to introduce Dave Wong (Daniel Wu), a psychologically disturbed cop.
Through narration addressed to no one particular, Dave resolutely but vaguely explains that his police uniform shields him from the fears that define him. He only announces this after Hon (Nick Cheung), a thief, is shown praying to demons and donning a mask before his next heist. That juxtaposition is tantalizing: Like Dave, Hon treats his work clothes as armor.
Their connection is further confirmed when Dave gives Hon a blood transfusion, not knowing who Hon is, or that Hon just killed two policemen. Feeling responsible for saving Hon’s life, Dave becomes obsessed with capturing him. But after this intriguing setup, Lam and Ng careen from one subplot to another. And thanks to Lam’s serial abuse of extreme close-ups, frenzied action scenes, and hideous expository dialogue like, “Luckily, we have the diamonds. Too bad we didn’t get what he owed us,” That Demon Within often feels like a berserk plot-vending machine.
For example, Liz (Christie Chen), an emotionally distant superior officer and largely undefined supporting character, discovers that Dave was abused as a child. Liz comes off like an accidental tour guide, making That Demon Within feel like a needlessly frantic slog to an inevitable conclusion that can be seen from a continent away.