Tom's brother gets sick so he gets sent off to live with a childless aunt and uncle. He is convinced it will be a boring time, but he discovers when the old grandfather clock downstairs strikes 13 at night, if he goes out the backdoor, he will find himself in a huge garden. He visits every night and makes friends with a girl named Hatty. She can see him, but it seems like others can't see him. Weird thing is that each time he goes through, Hatty has aged. It's not really noticeable at first.

Eventually, Tom learns that the old woman upstairs is Hatty as an old woman.

Good story. Not really a big conflict or anything.