On a drunken night out with friends in the seaside town of Leigh-on-Sea, widowed teacher Sarah unwittingly creates a séance. Sarah and her son Alfie are then subjected to a terrifying series of hauntings and Sarah becomes convinced that the ghost is that of a 19th century Sea Witch and namesake, Sarah Grey.

Sarah delves into the local legend which tells of how the witch made her living from the pennies that sailors threw her for a good wind. Allegedly, when the Captain of The Smack forbade his men to give her money, she cursed the crew and every man bar the Captain then perished in a violent storm. The Captain swore vengeance on the witch and the next day her headless body was found, in a bleak spot known locally as the Drowning Pool.

Sarah discovers that her much-derided and irritating Headmaster, Andrew, has his own reasons for uncovering the origins of the legend and together they attempt to get to the bottom of the centuries-old mystery. When a series of old letters surface, Sarah discovers that nothing and no-one is as it seems, certainly not Andrew and maybe not even the ghost of Sarah Grey...