In Glasgow, the drifter of few words Joe Taylor is working in an old boat with the sailor Les Gault and his wife Ella Gault transporting coal and other cargoes through the River Clyde. While loading the hold with coal, they find the body of a young woman wearing petticoat floating on the river and they bring it to the harbor. Joe recalls through flashbacks his relationship with his former mistress Cathie Dimly, while he seduces Ella in a carnal attraction, having sex with her in the absence of Les. When the police arrest a suspect of the murder of woman, Joe becomes interested in the case, while his thoughts disclose the truth about the death of the victim.