Marcel Dalton is the Dalton Brothers' Swiss uncle. He is not only honest, but a banker to boot. Having purchased a small bank in the US, he decides to hire his nephews to force them to make a honest living. Although he's assisted by Lucky Luke, they have their work cut out for them. Especially since – as if the ingrained instincts of the four dumbest bandits in the West weren't enough – there's also the small matter of the competition: a very unscrupulous banker ...