Clark was a maintenance workman, who, along with Hickman, was in the middle of converting an abandoned sea-fort in the English Channel into a sonar testing station. They were attacked by Sea Devils, who killed Hickman, and when the Third Doctor and Jo Grant arrived, he was frightened nearly to insanity. He dubbed the reptiles "Sea Devils".
After they were rescued, Clark was taken to the sickbay at HMS Seaspite. Jane Blythe later reported to Captain John Hart that "he was babbling something about Sea Devils". (TV: The Sea Devils)
Behind the scenes
In the novelisation, he is given the first name of Alan.
