Technically Once a Cop is a sequel to the 1992 Supercop, which teamed Jackie Chan with the equally acrobatic Michelle Yeaoh, but in spirit it harks back to the martial-arts costume epics of the 70s that featured virtuous women warriors torn between duty and love. It's also a vehicle for Yeaoh, who reprises the role of Yang, the tough police detective from Canton. Her boyfriend, a Chinese Vietnam vet disillusioned with penurious public service, has gone off to Hong Kong with his buddies to make a quick buck. Soon enough Yang too ends up on the capitalist island, helping local police investigate a series of vicious bank holdups with mainland connections, and finds that her boyfriend is now a leader of the gang. What ensues is betrayal and duplicity almost worthy of Hitchcock as the lovers try to reconcile and are pulled apart by their various allegiances. There's a tenderness and sexual tension among the three leads, and a prolonged finale with enough ammunition and grandeur to rival John Woo's pyrotechnic excesses. Directed and choreographed by Stanley Tong (and no doubt supervised by Chan), this thriller carries an indirect political message as well: the chief villain who wants to plunder Hong Kong is a Brit. And, yes, Chan himself shows up eventually, wearing a lovely pink outfit and impossible high heels. Film Center, Art Institute, Columbus Drive at Jackson, Saturday, February 5, 6:00, and Sunday, February 6, 4:00, 443-3737.