Number One with a Bullet (1987)

After a string of bad luck with their undercover operations, a duo of narcotics cops realizes that there must be a mole in their department, and their suspicion falls on their own captain, who never gives them a break. Nick, the hothead who's still in love with his ex-wife, is determined to prove that a local respected businessman is the head of the organization. But his pragmatic & debonair partner, Frank, agrees with the entire rest of the police force: Nick is crazy. After a forced vacation, they go a little beyond the law to bust the crime boss & find the mole.