A vicious bunch of thugs and a young couple in love. Lynch and Graham are involved with both while their own working relationship reaches flash point. PC Sweet and the relative newcomer DC Hicks also get caught up in the action.

The crew of a merchant ship about to dock at Seaport are looking forward to shore leave. They have money to burn and an itch to burn it in Rosie's Club. When a smallpox scare leads to all leave being stopped, two sailors have other ideas and sneak ashore. Lynch and Graham have to find them to prevent a possible smallpox epidemic.