Mystery of The Tower

Gary, an American teenager, comes to England to stay with his British grandfather, the Chief Yeoman Warder at the Tower of London. He meets the other Yeomen Warders' children who live in the Tower, and learns what life is like behind the thick, thousand-year-old walls. But he also discovers that it is not as safe as they think: the cowled figures that haunt the ramparts are dangerous villains.