The tuna clipper Star-Kist prepares to leave San Diego on a four-month voyage under skipper Joachim Qualen. Many of the crew of twelve are of Portuguese descent and have reenlisted for this trip.
While working in a laundromat, the boys find a baby hidden among the linen. They soon find out that the baby, who is the heir to a fortune, has been abandoned by his mother so that her two evil aunts can't cheat her and the baby out of the inheritance. The boys determine to help the woman claim her baby's rightful inheritance from her aunts, who have hired gangsters to find and eliminate the girl, the baby and anyone who helps them.
The boys are working at the local boxing arena where their friend, Jimmy Higgins, is boxing. During a crooked match Jimmy is killed. The boys seek out his older brother, Johnny, a former boxer who gave up the sport rather than go crooked, and help train him to get back in the ring. They try to get him a shot at the title, and when they do the same crooked gangsters that were behind Jimmy's death try to get Johnny to take a dive.
A man wins $50,000 in a card game with gamblers, but is soon found dead and the money missing. Slip and Sach find the money near where the body was discovered, and soon find themselves the target of both the police and the gamblers.
The East Side boxing champion Muggs answers a challenge to a fight against the West Side champ but just before the match he is kidnapped. His friend Danny Lyons takes his place and wins the fight, only to have Mugs believe that Danny was responsible for his kidnapping.
A seemingly charitable soup kitchen operator (who moonlights as a criminology professor) uses his Bowery mission as a front for his criminal gang. Police attempt to close in on the gang as they commit a series of robberies, murders and bizarre experiments on corpses.
