Former curate Billie has moved on to a new path . . . as a priestess in the Church of Satan. Meanwhile, her friend Maggie has made a similar switch-from Satanist to church-bound do-gooder.

When a mysterious visitor is found in a cave, an ancient evil from the unknowable depths of the Pacific Ocean is hot on their heels . . . and so is Christmas! In the midst of the madness, Billie does her best to arrange an improbable Saturnalia truce between the churches of England and Satan.