The once inseparable duo of Marcus Burnett and Michael "Mike" Lowrey is coming apart: an aging Burnett has become a police inspector  while Lowrey, suffering a midlife crisis, is assigned to head up AMMO, a "young guns" group of millennial cops with whom he has nothing in common. Both of them reunite once again when a fierce cartel mob boss, whose brother they defeated years earlier, makes a retaliation effort on Mike just as both he and Marcus are about to officially retire.