While on an expedition to Egypt, Marcus found the Black Pyramid, the prison of the Osiran Sutekh. Sutekh killed him, but animated his corpse and used it as a vessel of his power. Scarman (or his body) returned home via a time-space tunnel contained in an Egyptian sarcophagus.
Scarman killed Ibrahim Namin, Sutekh's servant, and with a small number of Osiran service robots at his command set about doing Sutekh's will. He killed his brother Laurence, witnessed the destruction of the Osiran war missile, and travelled to the Pyramid of Mars with a possessed Fourth Doctor and Sarah Jane Smith to release Sutekh from the Eye of Horus.
Despite Sutekh being freed, the Doctor defeated him, after which he relinquished his hold on Scarman's body, allowing him to die. Scarman appeared to regain his humanity, saying "I'm free! Free at last...", in the moments before he collapsed, died and turned to dust.
His priory burned down and the site would become that of UNIT HQ. (TV: Pyramids of Mars) Scarman's remains were never found and he was believed to have been among those who perished in the fire. A newspaper report speculated that, by an unfortunate coincidence, he had returned home from Cairo on the night of the fire. (PROSE: Doctor Who and the Pyramids of Mars)