The Web Table was delivered to the Institute (MAG 35) and was moved into artifact storage (MAG 36). Sasha took refuge from Jane Prentiss's attack in that room, where she encountered an unknown figure. Not-Sasha can be heard for the first time after that, repeating the last words spoken by Sasha. (MAG 39). It is unclear what exactly happened to the original Sasha, but Not-Sasha says that it hurt (MAG 79) and she is considered dead (MAG 80).
Not-Sasha was debriefed by Jonathan Sims following Prentiss's attack, and Sims did not notice any changes when talking to Not-Sasha, other than noting she seemed to be showing signs of stress from the attack. Not-Sasha claimed that Sasha's recording during the attack was lost, and the other recordings on which Sasha's voice can be heard also disappeared following the attack (MAG 40).
When Jon explores the tunnels below the institute, he sees a white arrow pointing down a set of stairs (MAG 41). This is later revealed to have been drawn by Not-Sasha trying to entice him to explore further and potentially discover Jurgen Leitner living down there (MAG 80).
Following the statement made by Helen Richardson regarding the appearance of Michael, Sims asked Not-Sasha about "her" previous statement regarding Michael, noting that it had been lost following the appearance. Not-Sasha was evasive about re-recording her statement, and after she left Michael appeared and warned Sims that she was lying to him. (MAG 47)
Not-Sasha frequently has trouble with her computer malfunctioning to the point of unusability (MAG 49). This is later traced to be problems with it authenticating when connecting to external devices or systems (MAG 70).
Sims stumbled across Not-Sasha staring at the table later, where she described its pattern as a web instead of a fractal, and noted that the table may have caught all of them. (MAG 51) Following this encounter, Sims discovered that she has been spending time at Madame Toussard's Wax Museum every two or three days. When confronted about this, Not-Sasha claimed that she had a new boyfriend she liked to have lunch around there. (MAG 52)
She visits the Trophy Room taxidermy shop, a stronghold of her fellow agents of The Stranger, to supposedly do follow-up investigation when no one else wants to. She reports seeing nothing unusual (MAG 54).
Not-Sasha caught Sims going through her desk, looking for anything unusual. He claimed he was looking for the files on the Hill Top Road case; she reminded him of her request he not record her private conversations. Sims noted that photos of Not-Sasha and her boyfriend Tom looked suspiciously like stock photos. (MAG 57)
Not-Sasha participates in the intervention held by the archival assistants and Elias for Jon (MAG 60).
When Melanie King visits the Institute to continue her research on ghosts, Not-Sasha lets her into the archive to talk to Jon. Melanie recognizes that she is not Sasha James, but assumes she's just a new employee (MAG 63).
When Jon is exploring the tunnels on his own, he runs into Not-Sasha and briefly catches a glimpse of her being much taller than she should be. She claims to have forgotten her coat, seen the open trapdoor and come down to check if Jon was okay. She mentions it being hard to focus in the tunnels (MAG 68). He later sees her entering and leaving the tunnels on two more occasions (MAG 74).
When Melanie visits Jon again to make a statement, she asks where Sasha is, leading to confusion between them as Jon insists Not-Sasha is indeed Sasha and Melanie accuses him of gaslighting. This causes Jon to realize Not-Sasha may not be what she seems, and prompts him to research other statements on the Not-Them (MAG 77), eventually finding out how Adelard Dekker trapped it in the web table (MAG 78). When he destroys the table, the Not-Them is released and chases him, attempting to kill him. At this point, it tries less hard to look human; when Tim and Martin run into it, they think it looks like Sasha, but very stretched out. While it is taunting Jon, at one point it gives a brief "statement" about being trapped in the table, and reveals that it had been sent to "the house of its enemy" to gather information in disguise (MAG 79). It prepares to kill Jon, but is then trapped by Jurgen Leitner rearranging the walls of the tunnels using The Seven Lamps of Architecture - although he is not sure it can be killed, he hopes it is now trapped for a very long time (MAG 80).