Dr B. MacRannoch is in the Bahamas with her father who has moved there from Scotland because of asthma. She is a savvy and tough young woman who shows much independence of mind and spirit.
However, when Sir Bart Edgecome, a British agent who has been poisoned with arsenic, falls ill on his way back from New York, she becomes involved in a series of events beyond her wildest imagination.
Drawn into an espionage plot with multiple suspects, it is only the presence of enigmatic portrait painter Johnson Johnson on his yacht, Dolly, that saves the day. But nothing is quite as straightforward as it at first seems.