The Mystery of the Flying Express (Hardy Boys Mystery Stories Book 20)

iv, 217, [1] pp. 8vo. #20 in the Hardy Boys series. "The Mystery Of The Flying Express is Volume 20 in the original Hardy Boys book series published by Grosset & Dunlap. The same title has been used for two completely unrelated story lines. The original story line involves the 'Flying Express' railway. This railway passes close to a foreign spy camp hidden in a forest. The revised edition involves a Flying Express hydrofoil." -- Wikipedia