The light jar

Nate and his mother are escaping from his emotionally abusive step-father, Gary, but the run-down and abandoned cottage in the woods that his mother takes them to does not seem like much of a refuge; but when his mother goes off to buy provisions and does not come back Nate is left alone (except for his imaginary friend Sam) and afraid--until a mysterious girl trying to solve the clues of a long-ago treasure hunt turns up.