The Mystery of the Deadly Double — William Arden

Jupiter Jones has been kidnapped! But the desperate criminals have grabbed the wrong victim. Jupiter happens to look just like the son of an African prime minister. Jupe doesn't dare point out the kidnappers' error. For once, the leader of The Three Investigators in helpless.

It's up to the other investigators to make the right moves -- and fast. The freedom of an African country is at stake -- and so is Jupe's life!