Can a Mermaid Kill?, by Thomas B. Dewey (epub/Kindle/pdf)
So unmoving was the girl sitting on the wet rocks that, at first, she seemed a permanent feature of the rugged seascape. She was wearing an expensive evening dress and high-heel slippers. She seemed to be in a deep trance, her gaze fixed on the sea, motionless except for the tossing of her delicate blond hair in the morning breeze. And as his steps brought him closer, he thought he had never seen anything so strange, so lovely, so vulnerable ... until he caught sight of the gun in her hand!