Doctor Syn poses as a respectable vicar in Dymchurch at the turn of the 18th century but, he is actually the retired pirate Captain Clegg. Believed hanged in Rye, he is no longer being sought by the authorities. However, country life proves too tame for the good "Doctor Syn," and his attention turns to smuggling. He takes on a secret identity, "The Scarecrow," and leads a gang of smugglers known as the Marsh Men.
They travel Romney Marsh by night on horseback, sometimes using mounts painted with phosphorus to give them a spectral appearance, spreading legends of supernatural evil and menace. Although a criminal, Syn's appeal is almost like that of Robin Hood. He uses his ill-gotten gains to help his parish, and the King's Men sent to ferret out him and his men are hardly a sympathetic lot, even though they represent the forces of law.