Making up in firepower what it lacks in subtlety, Bad Boys II is a big, bruising addition to the summer blockbuster contest. Crass, derivative and profligate, the film is also tremendously funny and exciting, at least until it starts to take itself seriously.

Holding together the slender plot are returning stars Martin Lawrence and Will Smith, whose jazzy, lighthearted chemistry makes the film's sour elements easier to swallow. Lawrence plays Marcus Burnett, a Miami narcotics cop with a wife and family. Smith is Mike Lowrey, his playboy partner. As the film opens, the partnership is placed in jeopardy when Mike wounds Marcus during a drug bust. Marcus will get even angrier when he learns that Mike has been dating his younger sister Syd (Gabrielle Union), an undercover cop from New York.

By coincidence, Syd is after the same drug lord that Marcus and Mike have been chasing for years. When he is not smuggling Ecstasy from Amsterdam or muscling in on Miami's Russian-owned nightclubs, Johnny Tapia (Jordi Mollà) is shooting at the rats who are eating the millions in drug money hidden in his mansion. By posing as a money launderer, Syd hopes to gather enough evidence against Johnny to convict him once and for all.

Syd's scheme is almost undone by seriously psychopathic Haitians, who try to hijack money she has just laundered for Alexei (Peter Stormare), a Russian who deals drugs for Johnny. But gaining Johnny's trust may cost Syd her life, especially when pressure from Marcus and Mike forces the drug lord to flee to Cuba.

While the script is filled with dazzling action sequences and some first-rate comic routines from Lawrence and Smith, keeping track of the plot can be arduous. Realizing that the second hour essentially repeats the first, sometimes as parody, can help, but Bad Boys II isn't about connecting the dots anyway. It's about throwing money around so lavishly that even pointless transitions are shot from helicopters. And in a summer of memorable car chases, Bad Boys II ups the ante with some of the most ferocious stunts ever put on film.

When not riffing on John Woo or Jackie Chan, director Michael Bay offers enough innovative ideas to rewrite the action genre, or at least throttle it into submission. One 360-degree shootout is a model of sustained tension. Even more noteworthy is a shot that extends from a helicopter into a nightclub, a trick that's remarkable and irrelevant at the same time.

Bouncing between the action scenes and the comic skits, with a few choice bits from a hilarious Peter Stormare, works so well that you can forgive the high body count and Lethal Weapon ripoffs. That is, until the filmmakers decide to get serious, at almost two hours into the story. Puzzling miscalculations like this one could mean mixed word of mouth for Smith and Lawrence's big summer blowout.

--Daniel Eagan