In The Dark (DI Fawley Thriller, Book 2) - Cara Hunter

A woman and child are found locked in a basement room, barely alive.

No one knows who they are - the woman can't speak, and there are no missing persons reports that match their profile. The elderly man who owns the house claims he has never seen them before.

The inhabitants of the quiet Oxford street are in shock. How could this happen right under their noses? But DI Adam Fawley knows that nothing is impossible.

And that no one is as innocent as they seem . . .