1539, Liverpool. A pregnant novice nun, Agnes Moore, ejected from her convent, claims to have been attacked in the ancient chapel of St Mary del Quay by Satan himself. Her former abbess, Lady Katheryn Bulkeley, comes to her aid, but Agnes refuses to identify her lover. When a young priest is found dead in the River Mersey, his right hand hacked off, Katheryn realises that Liverpool harbours some disturbing secrets. Then Agnes is brutally murdered, followed by more deaths - mutilated corpses discovered in the churchyard. As Katheryn seeks Agnes's killer, she faces the most urgent questions of all - why has such evil come to Liverpool and who is the Devil's Priest?