Searching for answers about the carving on the TARDIS, the Twelfth Doctor and Bill came to the Renath Archive to try to identify it. Angered by the head librarian Matildus Galathea's snobbishness, Bill went outside to the Kaballus Quarter for some fresh air. Noticing Bill was the first to come in or out of the library in months, the Kaballus Kids captured Bill and told her that Matildus used to let them hang around before she behaved strangely and barred the kids. Bill showed them a photo of Matildus being grumpy, which revealed something strange around her head.
Returning to the library with the Kaballus Kids, Bill told the Doctor, Matildus and Sashana to stop whatever it was they were doing. Bill took a photograph on her phone which revealed Sashana's true form. Sashana revealed that she was psychically sowing doubt in Matildus' mind and blocking her memories so Sashana could sell off the library's collection after being handed custody of it. She began to fry the group's brains with her mind but was stopped after Bill summoned the Ristallian crater-hound Archie, whose simple brain couldn't be kept back. After Sashana was arrested, the Doctor realised the carving wasn't a symbol, but a coded message. The Doctor and Bill's next destination to break the code was to see Alan Turing. (COMIC: Matildus)