Grace Marwood and her husband, a hopeless hypochondriac, take a cruise where she falls in love with the ship's medical officer, young Dr Daventry. The two continue to meet chastely for several years, with Marwood's behaviour becoming ever more selfish and insufferable in the interim, until her husband finally becomes suspicious and accuses her violently of the adultery she has not in fact committed, provoking her to leave him for the man she loves. Meanwhile, the invalid's every whim is catered to by the mysterious well-educated footman Simpson, who is apparently prepared to put up with anything from his employer. But Marwood falls genuinely ill, and Daventry is the only doctor in England who may be able to save him... and the footman has a secret of his own...