Hardy Boys 15: The Sinister Signpost by Franklin W. Dixon

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.

• Author: Franklin W. Dixon 
• Publisher: Grosset & Dunlap
• Language: English
• Format: Hardcover
• ISBN: 9780448089157 , 0448089157
• Genre: Juvenile Fiction