Isobel Frazier, retired schoolteacher, but still snapping with energy, is suddenly confronted by a child stealing a bottle of milk from her doorstep. She discovers he is one of four children fending for themselves and their invalid father, after their mother Katie has left them. The eldest boy, Trevor, is practically head of the household. Together with Trevor's friendly music master, Alan, Isobel befriends the young family, but Cliff Broadbent is a difficult man, bitterly resenting his crippling disabilities. Gradually, Isobel becomes aware there is some mystery involved in Katie's sudden disappearance...