Joe, a rootless young drifter, finds work on a barge travelling between Glasgow and Edinburgh, owned by Les and his wife Ella. One afternoon they discover the corpse of a young woman floating in the water. Accident? Suicide? Murder? As the police investigate and suspect is arrested, we discover that Joe knows more than he is letting on. Gradually we learn of Joe's past relationship with the dead woman. Meanwhile an unspoken attraction develops between Joe and Ella, heightening the claustrophobic tensions in the confined space of the barge.