Memory worms were a species that fed off the memories of other organisms. The Eleventh and Twelfth Doctors encountered memory worms in Victorian London and the far future respectively. The Eleventh Doctor and Strax tangled with a memory worm that they later used to defeat Walter Simeon, who was possessed by the Great Intelligence (The Snowmen). The Twelfth Doctor used memory worms to perform a memory wipe on Clara, Saibra and Psi when they attempted to break into the Bank of Karabraxos (Time Heist).

The Snowmen

★★★★★

TX: 25/12/2012

Written by Steven Moffat    Directed by Saul Metzstein

The Eleventh Doctor meets his new companion Clara Oswald, a barmaid working at the Rose & Crown pub living a double life as a nanny in Victorian London. The Paternoster Gang (which formed after the events of A Good Man Goes to War) make contact with Clara and explain to her that the Doctor has retired… albeit not for long. Alien snow has arrived on Earth and sentient snowmen are terrorising the streets of London! The Great Intelligence has landed on this planet and Walter Simeon, its henchman, (played impeccably by Richard E Grant, who previously starred as the Doctor in the spoof The Curse of Fatal of Death and the animated adventure Scream of the Shalka) is aiding it in its scheme to conquer the world. This episode serves as both an origin story for the Great Intelligence and as a prequel to The Abominable Snowmen and The Web of Fear (from the Intelligence’s perspective, not the Doctor’s). The Doctor takes on the role of Sherlock Holmes and he and the Paternoster Gang investigate the GI institute. After the Ice Lady (an attempt by the Intelligence to manifest itself in human-ice crystal form) and Clara fall to their deaths, the Doctor and Vastra confront Dr Simeon, who becomes possessed by the Intelligence. The Great Intelligence tries to kill the Doctor, but the family mourning Clara’s death generates an emotional field that turns the snow to rain tears. The Doctor vows to find Clara Oswald, having now met two different versions of her that died in different circumstances in separate time periods. 

Time Heist

★★★☆☆

TX: 20/09/2014

Written by Stephen Thompson & Steven Moffat    Directed by Douglas Mackinnon

The Twelfth Doctor and Clara are instructed to commit a bank heist. They and two others called Psi and Saibra are told by a mysterious Architect to rob the Bank of Karabraxos, the largest bank in the universe. A recording includes messages from each agreeing to a short-term memory wipe, before getting instructions from the Architect to break into the Bank of Karabraxos and steal three items from its vault. These items include a gene suppressant for Saibra and a memory chip for Psi. After breaking into the bank using fake DNA and disguises, the group meet Miss Delphox who is in charge of the bank security. Within the vault, the Doctor, Clara, Saibra and Psi discover that their real mission was to rescue the female mate of the Teller, a creature that detects a person’s guilt and is used to guard the Bank. Director Karabraxos is a clone of Miss Delphox and she imprisoned the female mate of the Teller as insurance. The Doctor and Clara rescue the two Teller mates and give them a new home elsewhere.