Josh Larson was a saloon keeper in Eternity, California.
Josh, who was called Old Josh, met the Fifth Doctor and Peri when they visited his saloon. He though the Doctor was Dr Sebastian Rowley, and the Doctor went along with it. Josh told Peri that he was one hundred and ten years old, even though he looked like he was in his twenties. When he was eighty, a man had sold him an elixir that made him younger, and currently let him age about a year for every ten.
Josh took Peri to visit Iziah Brown and his wives. Iziah told Josh and Peri his family's secret: they had found the Fountain of Youth. They took Josh and Peri to the cave where they fountain was located. They were soon found by the Master, who was seeking to repair the injuries done to him on Sarn. When Peri spilled some of the fountain's water on the cave floor, dinosaur fossils turned into living dinosaurs, which began to attack everyone in the cave.
The party, except for Dana, escaped in the confusion. Back at home, they were attacked by the Master's hypnotised townspeople. The Fifth Doctor suggested they shock the people out of their hypnotism, so Josh juggled candlesticks, standing on one leg. When the townspeople recovered, he ordered them home. (PROSE: A Town Called Eternity)