Gambler Jack Morton is persuaded to invest his winnings in buying the wagon and stock of a snake oil conman, and so reinvents himself as Professor Cornelius Murgatroyd's, purveyor of a miraculous cure for rheumatism, travelling across the West making a precarious living from the gullibility of others. But one day his life is disrupted when he goes to the aid of a dying woman whose wagon has been attacked by robbers, and makes a promise that he will take her baby son to safety with the child's grandfather in Claremont, several days ride away. And so begins a series of adventures where Morton has to pit his wits against numerous adversaries to fulfil his promise and to stay alive.