In 1973, Stevens was part of a group of UNIT soldiers that defended UNIT HQ in London from the Gel Guards. Lethbridge-Stewart ordered the complete evacuation of the building after their weapons were found to be ineffective. Led by Corporal Palmer, the soldiers awaited further orders as the building continued to be surrounded. Lethbridge-Stewart directed the soldiers to maintain vigilance, but told them to attempt no further offensive action. (DW: "The Three Doctors")
Later that year, Stevens was among the UNIT personnel who travelled to Llanfairfach for the investigation into Global Chemicals. With a group consisting of Lethbridge-Stewart, Sergeant Benton and Private Betts, he observed the Royal Air Force's grenade strike against the giant maggots. (DW: "The Green Death")
Now promoted to corporal, Stevens remained in Central London after it was placed under martial law following the appearance of prehistoric reptiles. Under the orders of Sergeant Benton, Stevens and another UNIT soldier prepared a makeshift cell for the Doctor at UNIT temporary HQ. (DW: "Invasion of the Dinosaurs")
Stevens was played by regular extra and stand-in Leslie Bates, who had appeared in some capacity on the program as early as the pilot episode of "100,000 BC". The character was only addressed by name in "The Green Death". Like his other roles on Doctor Who, Bates's role as Stevens was essentially that of a"spear carrier", performing a minor function on the behalf of a character more important to the narrative or being used to fill out numbers in group scenes involving a greater number of UNIT personnel than usual.