|Family||Shirley Allerdyce (Daughter)|
Little is known about Margaret's background, aside from the fact she was born in the UK and later moved to Fortitude with her daughter, Shirley.
Margaret is introduced as a blunt and unsociable woman. She is shown to be short mannered with Julia Sutter whilst examining her son, Liam Sutter and addresses Governor Hildur Odegard is a condescending tone in regards to potential quarantine procedures. She is also critical and verbally abusive towards her daughter Shirley in regards to her weight. However, despite her personality she is shown to be dedicated and effective at her job, quickly concluding that Charlie Stoddart is not dead and working furiously to try and save him before he passes away in the hospital.
Later in the season, Allerdyce is attacked by her daughter after she becomes infected with the Ichneumon Wasp parasite. She is severely injured when her abdomen is cut open with a fork, and is unknowingly made the secondary host for the parasitic wasp larvae after it is deposited into her by Shirley. Margaret is discovered barely alive and is taken to the hospital. There, unbeknownst to the staff, the larvae begin hatching and consuming her from the inside. It is only when Vincent Rattrey and Natalie Yelburton come to visit her to investigate whether she is the link between Shirley and Jason's behaviour do they notice the hatched wasps exiting her body. When Vincent attempts to inspect closer, Allerdyce heaves, releasing a swarm of Ichneumon Wasp's into the room, and promptly flatlines.