When gambler Jack Morton invests his winnings in the wagon and stock of a snake oil conman, he reinvents himself as Professor Cornelius Murgatroyd, purveyor of a miraculous cure for rheumatism. Travelling across the West making a precarious living from the gullibility of others, his life is disrupted when he promises a dying woman that he will take her baby son to safety with the child's grandfather in Claremont, several days' ride away. Morton must pit his wits against numerous adversaries to fulfil his promise - and stay alive.