Young Dr. Martin West has just arrived to take up an important medical post on a British island colony in the Tropics which is on the verge of being granted self-government, and where corruption is rife. His chief, Dr. Garland, shows him over an isolation establishment for lepers on a neighbouring island which is to be developed. Soon he is involved in a conflict of personalities and a maze of violent events. At a fiesta, when the population goes crazy with joyous abandon and fancy-dress is worn, a masked murderer kills Dr. Garland's assistant. A second murder follows. Susan Anstruther, the girl Martin falls in love with, almost becomes the third victim. Then Martin goes on the warpath. For a time he finds himself with a lot of riddles and no answers, until Dr. Garland's glamorous wife Celeste gives a dramatic turn to events and precipitates the climax.