Fleming (Underwater War)

You may be looking for the Coal Hill student of the same name.

Mister Fleming was head of security on the Ocean Explorer, a submarine searching for special minerals on the planet Hydron. He had a dark secret. Rory found fish roe on the sub, which turned out to be a fuel source. When they had walked up the side of a water volcano, he finally revealed his plan to Rory and Jane Clancy. He was going to use the fish roe to make him rich. Some people didn't know he had visited the planet before, in the Marine Adventurer, but all the crew had been killed except for him. Escaping with the fish roe in the submarine, he was almost away when the Eleventh Doctor saved the day. He was arrested and taken to the brig. (PROSE: The Underwater War)