At the Plume of Feathers in south Devon one midsummer evening, eight people are gathered together in the tap-room. They are in the habit of playing darts, but on this occasion an experiment takes the place of the usual game - a fatal experiment which calls for investigation.A distinguished painter, a celebrated actor, a woman graduate, a plump lady from County Clare, and a Devonshire farmer all play their parts in the unravelling of the problem...