The Locked Room by M.D. Spenser

Before, Brittany was just hurt and confused. Now she's scared to death. First, her mother and father were divorced. Then her mother married another man. A very frightening man ... It's a horror show race against time as Brittany and her little brother battle their fear. They must find out exactly why that man loves their mother. And save themselve from THE DANGER BEHIND THE DOOR . . . Book five in the popular Shivers series of scary books for kids.