In Bigg City Port there are two tugboat companies - The Star Tugs owned by Captain Star and the Z-Stacks, owned by Captain Zero. The Stars are honest and hardworking, but their rivals, the Z-Stacks are not to be trusted and often cause trouble. The Star Tugs hate foggy weather and one foggy, wintry day Scuttle Butt Pete makes them all even more nervous with his sea stories of strange things that happen when fog is around. Then, later that night, Big Mac sees four ghostly white tugs silently crossing the harbour...