The Angelic Avengers - Penguin Modern Classics

Lucan has been orphaned and Zosine has been deserted. Bound together by poverty and grief, they set out to make a future for themselves. They are adopted by the Reverend Pennhallow and his wife, and become immersed in study. But, after a chain of disturbing events, they realize that the cleric and his wife are not all they seem to be.