Lucan has been orphaned and Zosine has been deserted, and London is a hostile place for two young girls without a home. Bound together by poverty, grief and their shared years at school, they set out to make a future for themselves in new surroundings. They are adopted by the austere, puritanical Reverend Pennhallow and his wife, and in their large, gloomy house they become immersed in study. But, after a chain of disturbing events, it does not take long before they realize that the cleric and his wife are not all they seem to be.