The Jewel Smurfer (Smurfs Graphic Novels Series #19)

On the road leading to the town of Abelagot, two humans, Adhemar and Godillot discover an unconscious Jokey Smurf and take him along with them. After arriving in town, they meet a stranger who proposes to them to get rich by means of Jokey Smurf through slipping him into houses by night and forcing him to bring back the rich inhabitants' jewels.