In the course of investigating case #0150409 (MAG 16) Martin went to Carlos Vittery's flat at Boothby Road in Archway. No one answered the buzzers and he went to look for an alternative entrance. He saw a window into the basement, outside it was a silver worm, about an inch long with segmented skin and a black head. It charged at him as he approached it and he squashed it.
The basement itself ran under the whole house and smelt musty, with the air full of thick dust. It also looked like his shadow was moving in the dim light. In the building above, he knocked on Carlos' old flat, and was greeted by a woman in a headscarf who didn't speak English. She gestured to a man, Yassir Kundi, and closed the door. Yassir was the owner of the flat and confirmed that Carlos lived in the flat but that he was a recluse, and that Major Tom, his cat, lived with the Sanderson couple in number 2 now.
Martin returned to the Magnus Institute that evening. When heading home he decided to go back to Boothby Road to check the spider webs in the basement. When he returned, the spider webs were old, but swinging his torch around he saw a woman standing with her back to him. She had long black hair and a grey overcoat and coughed, or spluttered, into a green handkerchief. When she did this, one of the small worms fell out of it onto the floor.
Although she didn't react to the light, she heard Martin and turned around. Her teeth were black and cracked and as she removed her overcoat, Martin saw that her grey skin was covered in small holes, in which hundreds of the small silver worms crawled. As she stepped forward they all spilled out in a wave. Martin tried to take a photo, but managed to drop it as a worm leapt up at him. He fled out of the house and back home to Stockwell.
The next morning (or possibly the morning after), he awoke to a knocking on the door. He was about to open it before he remembered the woman. Spotting a small silver worm, he crushed it before blocking up any gaps that the worms might be able to get in.
He spent the next 13 days in his flat, unable to contact anyone, living on tinned or ready meals. He recalled learning about Jane Prentiss, the woman from case #0140912 (MAG 6) who attacked Harriet Lee. He recalled that Jane had claimed to be a practicing witch and believed she had been infected by an unknown and dangerous parasite. The knocking continued whilst he waited in the flat, but Jane never made any attempt to knock down the door or talk. The musty smell continued.
One morning, the knocking had stopped and after Martin carefully checked that she had gone, ran to the Magnus Institute.
Post-Statement Follow-Up Edit
Jonathan Sims offered Martin a sealed room to stay in in the Archives, and said he would ask Elias Bouchard to increase security. He also explained to Martin that he had been getting texts from Martin's phone, saying he was ill or may have caught some parasite, presumably from Jane.
As they spoke, Sims received another text from Martin's phone, saying, "Keep him, we have had our fun. He will want to see it when the Archivist's crimson fate arrives." Sims resolves to get better security in the Archives and to tell Tim and Sasha about what happened.