Cory had suspicions when he received reports of Dalek-like ships near Kembel. To carry out his mission, he commandeered a spacecraft and, without revealing his suspicions to his superiors, crash-landed on Kembel with crew members Jeff Garvey and Gordon Lowery, who did not know the true purpose of their expedition. There, he was proven correct as Garvey had become infected by a Dalek-created Varga plant and made into a homicidal creature. Cory informed Lowery of the mission. Cory was forced to kill him, just as he had already killed Garvey.
Marc Cory discovered the Dalek base on Kembel and the Galactic Council against the solar system. He recorded a message warning of the Dalek plot to destroy the sol system but was himself later exterminated by the Daleks before he could transmit his emergency message to Earth. (TV: Mission to the Unknown)
Bret Vyon and Kert Gantry went to Kembel to find out what had happened to Cory. The Doctor found Cory's skeletal remains, as well as the recorded message warning the Earth of the Daleks' plans. (TV: The Daleks' Master Plan) When the message was returned to Earth, it exposed Mavic Chen and Karlton as traitors, conspiring with the Daleks. While Chen was already dead, Karlton was arrested by Senator Diksen and was put on trial for high treason. Disken told Karlton that "the dead would have their revenge yet". (PROSE: The Mutation of Time)
In the early stages of the Great War which immediately followed the Time Destructor disaster, (PROSE: The Evil of the Daleks) Cory's good friend and fellow agent Dryn Faber successfully destroyed a Dalek drilling station on the ocean planet of Antalin as an act of revenge for Cory's death. (PROSE: War of the Daleks)
Behind the scenes
- As no regular cast members appeared in Mission to the Unknown, Marc Cory essentially acted as the hero of that story.
- Peter Hawkins was the voice actor for Marc Cory in The Daleks' Master Plan, for which he remained uncredited both on-screen and in Radio Times.
- Terry Nation described the character as "a space age James Bond".