Sharkey was an informant in 1940 London.
While talking to the Seventh Doctor, he managed to steal the dormant Cybermat he had in his pocket. He later offered to sell it back, and dismissed the Doctor's warnings of how dangerous it was. Other Cybermats chasing Ace where subsequently attracted to the one in his pocket when they reached Mama's American Bar. They attacked Sharkey instead, killing him. (PROSE: Illegal Alien)