The Sinister Sign PostBook - 1968
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.
Publisher: New York : Grosset & Dunlap, 1968
Characteristics: 175 p. :,ill
Alternative Title: Sinister signpost