Tintin and Captain Haddock are sent to guard Professor Calculus, who has invented a machine that can duplicate anything, and is staying in a village near the border of Syldavia and Borduria. However, an infamous and ruthless international criminal tries to lure Calculus and Tintin away by kidnapping two children, who live nearby, in order to get his clutches on the machine.

Lily is a lost girl who lived a miserable childhood. Now she works for Martial, a small-time crook. One day, she meets Armand, a shy high school student, the son of a renowned surgeon. And she discovers true love. But Martial is nothing of a tender heart, on the contrary. He manipulates Lily into forcing Armand to mimic the signature of his father, which will allow his gang to obtain drugs with a view to selling them...