Doctor Mark Mathias was a junior attending physician and friend of staff nurse Thomas Hector "Hex" Schofield who worked with him in the accident and emergency department of St Gart's Brookside Hospital. He was manipulated by Hex and Ace on 12 October 2021 after he was taken by the Cybermen. (AUDIO: The Harvest)

Hex later inquired about him during the 2025 London evacuation. Oracle informed Hex that Mark was infected with "the contagion", and transformed into a zombie. Hex had thought that he'd return for him, and that he and Mark would go for a drink at the White Rabbit like in the old days. (AUDIO: Project: Destiny)

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