The Night of the Amnesiac - S3.E22

A stage coach carrying the western states entire supply of smallpox vaccine is attacked and the drug stolen. Furman Crotty, a convicted criminal serving time in Leavenworth, is demanding his release from jail with a full pardon and a ransom for the safe return of the drug. While Jim West, injured in the attack on the stage, struggles with amnesia, Artemus tries to find both his friend and the drug before a full-scale epidemic hits.