Who is behind the burglaries in the villa district? The three ??? help Commissioner Reynolds search for the culprits. Although the area is monitored by patrol cars, the thieves manage to mysteriously disappear quickly. During a nighttime patrol, the detectives and the commissioner observe ghostly figures fleeing on horseback with stolen goods. They can't make out anything in the photos since the horses are covered. However, they discover a riding stable nearby. Could the horses have come from there? Undercover, Justus, Peter, and Bob begin their investigation and learn a lot about riding and horses in the process.