Sean was an Irish sailor who was shipwrecked near Atlantis. He was captured and put to work in the mines. He and Jacko met Jamie McCrimmon and Ben Jackson when the last two were assigned to the mines. The four of them escaped and met with the Second Doctor to aid in his plans to defeat Professor Zaroff. Sean and Jacko's job was to convince the fish people to go on strike, leaving the Atlanteans without any food. After the Doctor flooded the lower levels of Atlantis, Sean and Jacko fled to the surface, where they saw the TARDIS dematerialise. (TV: The Underwater Menace)