Hurrying along a lonely road on a rainy night, Dr. Jervis, a young medical student and practitioner, discovers the body of a man, apparently dead, lying partly concealed in the hedgerow. He hurries off to summon the nearest constable and together they return to the spot, only to find that the body is gone. Jervis makes a few inquiries, but they lead nowhere and the incident is forgotten.
Yet from that night the young doctor is a marked man, stalked by an unseen enemy of fiendish cunning. Innocent of any crime and without suspicion as to who this malicious and invisible enemy may be, Jervis is an easy prey and several times escapes death only by the narrowest margin. Finally Dr. Thorndyke, senior associate of Jervis, seriously attacks the problem and the battle of wits is on.