Andrew, who receives a spyglass, black notebook and detective badge for his eighth birthday, has trouble solving the mystery of who has left, on three successive nights, a paper-wrapped glob of mud in his shoes, white ""ghost footprints"" on his bedroom floor, and two turtles (just what he always wanted) in a box by his bed. Readers, however, will suspect scoffing older brother Tom from the start -- that is, if they care about tracking down such a benign, uninventive and prosaically depicted ghost at all.