Night of The Hunter; by Davis Grubb.

A stupendous courage and sharp intelligence, not to mention the responsible way of behaviour, is stamped on the story in the way a little boy of hardly ten saves his own and his sister's life from the man that has arrived supposedly with a message from their father and supposedly a friend of his, but in fact with a clear and definite intention of taking the treasure he suspects them of hiding and killing them. The stranger does manage to fool the mother of the two children he has met as a fried of her husband into marrying him, and the little girl is all too credulous of the love of a father figure since she is missing her own loving father. But the boy - boy oh boy - he is perceptive, sharp, careful, naturally suspicious of the predator, and again, courageous and responsible, in the way he manages to save himself and his sister against all odds from being killed by the vicious stranger.