Hercule Poirot and his associate, Captain Hastings, are called in by his eccentric mystery author friend, Ariadne Oliver, to a manor house in Devon. Oliver is organizing a "Murder Hunt" game for a local fair to be held at Nass House, but she is troubled by something she cannot quite put her foot on.
Things take a turn for the worse when during the "Murder Hunt" the girl playing the "dead" body is murdered for real. Soon afterwards, the lady of the manor mysteriously disappears and an old man's body is pulled from the river. Poirot must discover who and what are behind these seemingly unconnected events.