Dry wit and nautical lore run through this mystery - Lady P is a scientist, inventor and engineer and above all she's a fun-loving and youthful grandmother. But she doesn't see the funny side when the dead body of a youngish woman turns up on board her daughter's sailing boat. Even Inspector Plummer cannot prevent Lady P's natural inquisitiveness landing her in deep water and in hospital. But gradually clues surface with very unpleasant ramifications for all concerned.