It's the start of the 1860s, and the Old West is changing-a change that comes as a shock to the Daltons when they're arrested not by Lucky Luke, but by... Allan Pinkerton! The man is determined to turn bandit-hunting into a modern, rational business-even at the cost of the American people's personal freedom. It'll be up to Lucky Luke to ensure that the USA is protected against all evil-doers, rascals and lawmen alike...

After their umpteenth defeat at Lucky Luke's hands, the Dalton brothers get into a big argument that ends with the four of them splitting up. They make a deal: Whoever is first to get a million dollars will be the leader of the gang. Going their separate ways, trying various schemes, each spreads his own kind of mayhem, forcing poor Lucky Luke to do four times the work to keep up with their antics !