Brothers Adolph and Arthur Caille are mechanical geniuses. They've just created one of the first slot machines and have presented it to their local senator, a notorious gambler. Much taken with the device, he agrees to send them on a tour of American cities to test the machine's popularity. And, to escort them on this dangerous journey, he calls on his old friend Lucky Luke - So begins the wacky tale of how the one-armed bandit conquered the West!