Johnnie To and Wai Ka-Fai's co-directed policier Mad Detective has a lot on its mind, though a certain baseline ludicrousness keeps it from being as effortlessly entertaining as To's best. Lau Ching-Wan plays a master sleuth whose working methods require him to reenact crimes from the perspectives of the perpetrator and the victim. After a decade or so of cracking impossible cases, Lau has become an unreliable nutcase, booted from the force because he won't stop talking about how he can see the multiple personalities inside everyone. Then young cop Andy On enlists Lau to help track down a missing cop, and the two of them enter a weird cat-and-mouse game complicated by the fact that the veteran, the novice, and their mutual prey all spend a lot of time talking to their "inner ghosts."
To and Wai illustrate those ghosts by having separate actors play them, which means at times, the screen is filled with 10 or more people, all representing two or three actual characters. Once viewers figure out what's going on—which takes a scene or two—the gimmick isn't that hard to follow, but it always looks strange to have, say, a 12-year-old boy, a middle-aged woman, and an old fat guy all yelling back and forth and pointing weapons at each other across a tight, shadowy room. (The psychology also seems a little suspect.)
Fleeting confusion and bizarre literalization aside, though, Mad Detective is an effective mystery story, with an oddball hero—like TV's Monk, but far crazier—and some moments of visceral violence that raise the stakes. Mad Detective is short and lean, and has a point to make about the different reasons why personalities fragment. For Lau, it's a function of trying to solve crimes and effect justice. For On and everybody else, it's all about the petty ways they try to cover their asses and save their jobs: by lying, making excuses, and generally becoming something other than the best version of themselves.