I’ll go ahead and call "Drug War" the best Hong Kong action movie since "Infernal Affairs" (the 2002 film that Martin Scorsese remade as "The Departed"), even though technically it’s a Chinese film.

But the director, Johnnie To, here making his first action film in China, and lead actor, Louis Koo, are both Hong Kong natives; and they’re at the top of their game in this thriller about an important link in a drug chain who, rather than face the death penalty after he is captured, instead turns informant.

Or does he?

‘DRUG WAR’ Not Rated Opens today at Pearlridge West 16 and Dole Cannery Stadium 18; in Mandarin with English subtitles

Koo is Timmy Choi, whose factory is busted by a group of vice cops led by a Captain Zhang (Sun Honglei, a veteran mainland Chinese star). Facing certain death (China’s laws are not very forgiving), Timmy agrees to lead Zhang through a maze of contacts and underground drug pipelines to expose the whole network.

Trouble is, Zhang begins to feel he is being set up by Timmy, who appears to be leading Zhang onto a dangerous cat-and-mouse game.

Koo delivers such an effective performance that it’s hard to guess what his motives are until the end. The director ("Mad Detective," "The Mission") is one of Hong Kong’s best action maestros, but less reported is his excellent grasp of tension and suspense.

As always, To delivers fantastic set pieces — an opening scene of undercover cars tracking a bus through a crowded toll booth line is a good one, and there’s a complex shootout in a drug factory run by mutes who can communicate with each other more effectively than the police with their radios can.

Best of all is a harbor scene in which an undercover cop gets an entire fishing fleet to set sail at once, an example of how To can rise to the challenge of any sequence.