Sherlock Holmes is fending off a particularly dark mood as he roams the Sussex Downs, in search of wild bees. The Great War may be raging across the Channel, but on the Downs, the great detective nears terminal melancholia -- only to be saved by an encounter with headstrong, yellow-haired young Mary Russell, who soon becomes the Master's apprentice not only in beekeeping but in detection. Holmes instantly spots her remarkable ability, but his sharp eyes also see troubling problems. Why is this wealthy orphan who lives with her aunt so shabbily dressed? Why is she so prone to illness and accident? Is she herself the center of a mystery? These are questions that the great detective must answer quickly lest his protégée, and his own new lease on life, meet a sudden tragic end.