In 1893, the mysteries of the world are on the brink of being solved. Fossil hunters claw the remains of prehistoric beasts from the cliffs of southern England. The safe securities of Biblical history are brought into question by the realisation that the earth is far older and wilder than had ever been imagined. And yet all the reason in the world can crumble in the face of superstition. Down in the marshes and estuaries of Essex, something moves in the dark waters and legends of a half-forgotten, terrifying beast start to surface once again.