When the members of a caravan of pioneers find a daisy growing in the middle of the desert they decide to stop there and to build their town on this very spot. Houses soon spring up like mushrooms, immediately followed by a bank, a saloon, a prison, etc. Daisy Town is born. Unfortunately a city does not go without its bad boys and the peaceful place is soon turned into a lawless place. To restore law and order, a lawman is needed. Lucky Luke, the cowboy who shoots faster than his shadow, will be this man: all the villains had better watch out!

The story opens in a Western saloon, where a young musician with a banjo begins to tell a tale of Lucky Luke and his sworn enemies the Dalton brothers: Joe, William, Jack and Averell. Luke has, once again, as he has done many times before, thrown the four outlaws into jail. The prison is also the abode of a guard dog named Rin Tin Can (Rantanplan in the original French language version).

Lucky Luke becomes the Sheriff of Daisy Town and runs out all the criminals. Then the Dalton brothers arrive and try to get the Indians to break the peace treaty and attack the town.