Reprising the setting and some of the plotlines of The Hound of the Baskervilles, Holmes and Russell come to the aid of the Reverend Sabine Baring-Gould.

The book opens with Mary Russell receiving a telegram to come immediately to Devon and to bring her compass.

Initially Mary is reluctant to abandon her academic studies in Oxford to assist Sherlock, but she finally complies.

This tug and pull of the two individuals in their own professional lives erupts throughout the book to show each person's independence, yet reliance on each other.

The way that Holmes reacts to the many mentions of the original case, with a mixture of pride and exasperation, allows for some very humorous moments.