In one of the most dangerous and intriguing cases of their careers, Frank and Joe Hardy help their father investigate a series of mysterious car accidents.
Each of the drivers had seen a signpost marked DANGER shortly before his accident.
The young detectives investigate, only to discover that the signposts have vanished.
The attempted theft of a secret experimental motor and the kidnapping of a famous race horse are part of this thrilling case, which proves to be as sinister as the signposts themselves.
Grosset & Dunlap Hardy boys 15: the sinister signpost, hardcover/franklin w. dixon
