FBI special agents are called in to capture the notorious bank robber and kidnapper Alvin Karpis, the machine gun blasting thug who provides the muscle for the infamous Karpis-Barker gang. Federal heat forces Karpis from hideout to hideout but Karpis always stays one step of the FBI. The G-men play their trump card and, knowing that the gangster loves fishing, manage to track their quarry to popular pier.