Sapphire & Steel (1979)

Season 3: Episode 4

Once Silver concocts a way inside the capsule, he transports Sapphire and Steel into the experimental pod from the future. The couple are no where to be found but Sapphire, Steel, and Silver come face-to-face with the adult-sized infant. Sapphire deciphers that the overgrown baby is a changeling controlled by time. The changeling senses that the three time agents are a threat and the force controlling the changeling commands that he destroy them.