The surrounding land of Daisy Town is divided between farmers and cattle owners. Luke doesn't worry about this until a certain Mr. Josephs wants to sell barrels of gun powder. Helped by Laura, a young farmer, Luke discovers that Mr. Josephs is in fact Joe Dalton... Luke and Laura are captured in an old mine shaft and the Daltons start their vendetta.

The Dalton Brothers Ma takes a liking to Lucky Luke, causing her son Joe to become jealous. This sets the plan for him and his brothers to escape from jail. To attract their mother's attention, the four brothers plan to rob all the banks in the area, dressed up as Ma Dalton. Who would shoot an old lady? In Daisy Town, Luke is informed about the plan...