One might assume that Marcel Dalton is the long-lost fifth member of the gang of brothers; however, that is far from the truth: He is Ma Dalton's brother, a banker, and also a Swiss with more than just a slight accent. This Dalton has his brothers released from prison with the blessing of a senator and the help of Lucky Luke. One would like to see if they are capable of honest work in a bank purchased in America. Of course, things go awry. Thus, Lucky not only has to battle the local banker James Swindler but also capture his eternal adversaries once again...