On a cattle drive to New Mexico, Lucky Luke travels through Langtry, home of self-appointed judge Roy Bean. A crook and a cheat who invents laws and concocts offences, Bean arrests Luke and confiscates his herd. But he doesn't count on the arrival of another crook and cheat intent on poaching the old man's game. It will be up to the world's favourite cowboy to sort it out and bring real law west of the Pecos River at last.