Fifth in the Chrestomanci series, a young adult fantasy series about parallel worlds and the magic users able to move through them. In this book we meet Conrad, sent by his uncle to infiltrate the great house at Stallings as an apprentice valet, where he meets Christopher, the apprentice to the great magician Chrestomanci, also acting as an apprentice valet while he searches for a missing friend. Two young boys, a Downton Abbey-like backdrop, and sinister magical goings-on to investigate... pretty typical YA theme but well executed.