The first night in his bedroom in the new cottage, Jack is thinking about Denton, his best friend.  Ned becomes very nervous.  Nothing would calm him down.  And then Nathaniel Witherspoon appeared.  Nathaniel  is a ghost, the ghost of Lizard Light.  Nathaniel tells Jack, "You're exactly the boy I need."

Nathaniel and Jack become friends and explore the beach and the lighthouse after Jack's parents are asleep.  On a field trip to the Minty Museum, Jack discovers an old rusted knife with a whalebone handle.  This knife turns out to belong to Nathaniel's father, who died at sea over 150 years ago.  This knife opens up a mystery that Jack and Nathaniel work to solve.

I don't really like scary books, but Nathaniel is a friendly ghost and it is almost as if he were real.  It was really a good book.