By chance, members of the Detective Club learn about the existence of an ancient talisman that once belonged to a robber named Duke. Two hundred years ago, fleeing from his pursuers, a robber hid his jewel somewhere... Deciding that this case is a real find for young detectives, Holly, Tracy, Belinda and Jamie set off in search of the missing talisman. But they don’t even imagine that a real criminal is hunting them - cruel and merciless, and their paths will soon cross...