Lucky Luke has just led a herd in Louisiana, New Orleans. In a saloon, he meets two captains in the process of settling their accounts. Lucky Luke takes the defense of Captain Barrows. Captain Lowriver, a true pirate of fresh water, has put himself in the lead to ensure the navigation on the Mississippi between New Orleans and Minneapolis and has already deterred many sailors. But Barrows stands up to him. Lowriver offers to Barrows a race between their two ships with load and passengers and respecting all the ports of call. The first arrival in Minneapolis will have the monopoly of the river transit. Barrows accepts and engages Lucky Luke so that he can play the tricks of Lowriver. This navigation will not have anything to do with a pleasure cruise!