While on vacation, Ed Lucas presents his wife Kate with a souvenir of "The Concrete Captain," a small chunk of concrete with a miniature harpoon sticking out of it. Kate seems to be drawn to the item, continually picking it up and looking at it. Later, she is also drawn to a seaside inn where she and her husband hear the tale of the Concrete Captain and his wife, Katherine. But when Kate becomes ill and starts acting strangely, Ed wonders if the Concrete Captain hasn't returned to try to claim Kate as his own.