The Sea Devils are an ancient race who went into hibernation for thousands of years. They saw an object which was going to crash into the Earth. That object was just the Moon. The Doctor met the Sea Devils in a deserted sea base where they killed one man and left the other frightened for his life. They are tall, reptillian and have heat blasters. The Sea Devils were working with the Master. The Master used a signal machine to lead them onto the shore line but then went back into the waters. Except for one who followed the Doctor and Jo into a mine field. The Doctor used his Sonic Screwdriver to activate the mines. When the mines blew up the Sea Devil ran for its life and went back into the sea. Then the Sea Devils really attacked, they attacked the prison where the Master was kept and killed all of the guards and the Master's friend. The Sea Devils then invaded the sea army base and took it over. The Master and the Doctor were working on a time system to awaken the army from the bottom of the sea bed. The Doctor made peace with the Sea Devils but then the sea army attacked the sea bed with bombs. The Master told the Sea Devils about the humans were vicious. The Sea Devils declined their peace offer and locked the Doctor and the Master up. Then on the shore the Sea Devils were attacked and some were killed whilest others fled into the waters. The Sea Devils plan was working. There was a Sea Devil on a submarine but he was tricked and killed. The Sea Devil's base was bombed and them and their hibernation chambers were destroyed. Some of the Sea Devils bodies rose to the surface. The Doctor managed to get to the shore line but the Master escaped yet again.
The Sea Devils returned to fight the Doctor alongside their cousins the Silurians. Ichtar leader of the Silurians unfroze the Sea Devil army from underneath the sea bed. Sauvix who was the leader of the Sea Devils got his men ready to attack the sea base. When the attack began the Sea Devils attacked one side of the base and the Myrka attacked the other. The Myrka was the first to break through and it killed several people. The Sea Devils then followed in their bulletproof armour. They used their heat blasters and also killed several of the humans. The Silurians were behind them with their equipment. The Silurians and the Sea Devils now had control of the base. The locked up some of the sea base crew members, Tegan and Turlough. They had the commander and the Doctor on the bridge. The Doctor knew one of the Silurians from his last adventure with them. The Silurian he knew was Ichtar and the Silurian remembered the Doctor. The Doctor did manage to escape and find a weakness against the Silurians and the Sea Devils. it was extra crowminte gas which kills all reptile life. The Doctor needed a test subject and he got one. A Sea Devil got fired at with the gas and his whole face was flattened with its blood coming out. Then Sauvix entered and fired at the gas by accident killing himself and a woman friend to the Doctor. The Doctor released the gas into the ventalation ducts. In the corridors the Sea Devils were dying out. The Doctor had by then killed the Myrka. Then the Doctor warned the Silurians about the gas. They had already set the nuclear missiles to destruct as they wanted their planet back. The last of the Sea Devils had just died and so did the Silurians. Ichtar still put up a fight until Turlough shot him. The Doctor felt ashamed and thought their could have been another way.
The Sea Devils have appeared in:
Season 9: The Sea Devils
Season 21: Warrior's of the Deep