Matildus ( comic story ) Summary . Continuing their attempts to decipher the symbol left on the doors of the TARDIS , the Twelfth Doctor and Bill travel to the Renath Archive , an enormous library run by a woman called Matildus Galathea , underneath the spaceport of Cornucopia . Upon landing , the Doctor is immediately confronted by Matildus for losing a variety of books , but she begrudgingly accepts his replacements . After the Doctor explains about the symbol to Matildus , she recommends they visit the religious section of the Archive to investigate , but she begins to forget her words while talking , despite saying it is nothing . However , Matildus quickly gets relieved of her duties by the appearance of her granddaughter Sashana . As Bill takes the opportunity to take some photos of the history section , she questions Matildus on why it is so quiet , and quickly gets shouted at for not being the academic type that the Archive was intended for . Bill storms out , slamming the door behind her . Bill stumbles upon the bustling market place of Cornucopia and takes some more photos , not knowing she is being watched by a group of four . Meanwhile , the Doctor and Sashana are not able to make much progress , especially with the news that Matildus ' confusion has been getting steadily worse . At the market , Bill ' s phone gets stolen by a blue - skinned child in a cape and runs away with it , followed by Bill , causing chaos as she goes . The child eventually gets cornered into a dead end , but takes the opportunity to capture Bill in a tangle - web , revealing the group of four . The girl who stole Bill ' s phone identifies herself as Lozz , alongside her friends Zeddy , Sparks and Morpho - the Kaballus Kids . Bill proves her innocence of not being from Cornucopia by the photos in her phone , although Lozz summons a Ristallian crater - hound called Archie to double check , and he licks Bill ' s face , clearing her name . Lozz explains that they captured Bill because she was inside the Renath Archive , and nobody has been seen going in or out of there for months , although they state that Matildus used to be very kind to them . However , when Bill shows them a photo she took of Matildus , she notices a mysterious red swirl around Matildus ' head . Upon discovering nothing with Sashana , the Doctor goes to quietly wake up Matildus and tell her the news , but she temporarily forgets who the Doctor and Sashana are . Matildus decides to finally pass ownership of the Archive to Sashana once and for all , with the Doctor acting as witness . . . as Bill and the Kaballus Kids burst in to stop it . Although the Doctor is baffled as to why , Bill goes to reveal Sashana ' s true identity , but she changes herself , revealing herself to be evil all along . She announces that Matildus never actually had any family and she was there to slowly chip away at her mentality , take over the archive and sell it off , although decides to fry everyone ' s brains with a horrible noise instead . As everyone collapses to the ground , Bill just about has the strength the blow on the flute to summon Archie who is unaffected by the noise , and he tackles Sashana into a bookcase , knocking her out . Later on , the local police arrive to arrest Sashana , placing her in a Traulian dampening helmet to block her psychic powers . Although her mind is finally cleared , Matildus appears depressed that she has been lied to , ending up with no friends or family . However , the Doctor points out that she still has the Kaballus Kids , and he chuckles as she tells them off for running through the Archive . As the Doctor and Bill return to the TARDIS , disappointed at not figuring out the symbol , the Doctor suddenly remembers Matildus mentioning " the archivists ' code " and realises the symbol may have been a coded message all along . Back in the TARDIS , the Doctor leaps to the controls and starts setting off again . When asking Bill who in time she would ask to break a code , she jokingly suggests Alan Turing . The Doctor simply smiles knowingly at her , astonishing her that that is his actual plan . References . " to be added " Continuity . " to be added "