Eleven-year-old Roz (Rosalind) Anthony and her family have just moved to Mills River, Illinois, to escape an abusive situation. Only days after settling into their new home, they are surprised to find the previous owner, Tillie Monroe, on their front porch reading the newspaper. Though her sons have sold the house and sent her to a facility for the aged, she is determined to die in the place she lived her life, and somehow manages to find her way "home" day after day. Feeling sympathy for the elderly woman, Roz's mother allows Tillie to move back in.

Mara Nightingale becomes Roz's first friend in Mills River. In spite of their many differences, the girls discover they have something in common that binds them together--both are hiding secrets. So they make a promise--"cross my heart and hope to die"--never to tell anyone else.

When danger stalks the Anthonys, Tillie exhibits unimaginable courage and selfless love in her determination to protect the family she has adopted as her own.