The First Transcontinental Railroad is stopped dead near its starting point, both in the East and in the West. Repeated injunctions from the president of the Transcontinental Railroad are having no effect. His workers are constantly prevented from working by agents of a mysterious traitor. But Lucky Luke witnesses one of the acts of sabotage and stops it. Soon, he is in charge of security for the entire westward push - and he will have his work cut out for him.