“Drug War” screens at 7 p.m. Friday at the UW-Cinematheque screening room, 4070 Vilas Hall, 821 University Ave. R, 1:47, three and a half stars out of four. FREE!

Johnnie To’s “Drug War” opens with a man, burned and frothing at the mouth, losing control of his car and crashing through the front door of the store. We don’t know who he is or what’s wrong with him. Get used to that feeling.

To’s exhilarating and complicated police drama keeps the audiences at least a step behind on its plotting, showing us a detail or introducing a character and then only later explaining what it means. It’s an unusual and engrossing plotting technique in such a well-worn genre, but it mirrors the feeling of uncertainty of the film’s heroes, a crack team of police officers trying to break up a meth ring. They, like us, don’t know what’s waiting for them.

That injured man turns out to be Timmy Choi (Louis Koo), who was injured at an explosion in his meth lab that killed his wife and brothers. Manufacturing drugs is a death sentence in mainland China, and Choi is eager to avoid a lethal injection. So he agrees to turn snitch, leading the relentless Captain Zhang (Sun Honglei) and his team against the cartel he’s been cooking for.

At first, it seems like the police are more than equal to the challenge, and To stages elaborate setpieces that show off their cunning and preparation. In one bravura scene similar to the Dubai sequence in “Mission Impossible: Ghost Protocol,” Zhang intercepts a meeting between a supplier and a dealer, impersonating each party to the other one. In another sequence, we see a complicated drop at a traffic light, and a raid on a smuggler’s den that goes off flawlessly, climbing up the ladder to the secretive drug kingpin they know only as “Uncle Bill.”

But To keeps introducing bits of seemingly random visual information that puts us on guard a little bit. Specifically, the same characters keep showing up in the background — a bearded old man, a well-dressed couple — seeming to watch the action from afar. Whose side are they on? Are they on a side? All is eventually revealed, but their presence underscores that there’s a lot more going on than Captain Zhang and his team are yet aware of.

To is known for his spectacularly staged gunfights, and “Drug War” ends on a dilly, a protracted gun battle between cops and criminals that starts out in front of an elementary school and spills out onto a nearby highway. The action is crisply staged, but shocking in how quickly things spiral out of hand for Zhang and his team. This is a grittier sort of action film than I’m used to seeing from To, illustrated by the anonymous highways and streets where the violence takes place, often in pitiless broad daylight. Fans of Hong Kong action will find much to like here, as will fans of dogged police procedurals like “The French Connection.”