The one where the canon is on the verge of an "upgrade".
Written by Chris Chibnall. This episode first aired February 23, 2020.
In the far future, the Doctor and her companions track down a small group of human survivors from the CyberWars. As they try to protect them from forces led by the Cyberman fanatic formerly known as Ashad, the Doctor and her "fam" are split up, as are the survivors, trying to get to Ko Sharmus, where the Boundary that will allow the humans to escape this galaxy awaits.
In the past, a childless couple in early 20th century Ireland adopts an abandoned baby boy they name Brendan, who grows up to join the Gardaí as he wants to make a difference in his community. However, there's something unusual about him, as he survives getting shot and falling off a cliff by a robber he was trying to talk down, with no broken bones and the bullet not even penetrating his skin. He lives to old age and retires, only to be confronted by his adoptive father and the police officer who was there the day he was found, with the both of them the same age they were when he joined the Gardaí. They take him to a back room, where they restrain him in a chair and hook him up to a device that shocks him as they tell him he'll have to forget... again...
Graham and Yaz end up stuck on an old Cyber Carrier still housing a sleeping army as Ashad pursues them, reactivating the army and turning it to his own purposes. The Doctor, Ryan and a survivor named Ethan make it to Ko Sharmus in a stolen ship to see the legendary Boundary, only for the portal to lead to the ravaged Gallifrey after the Doctor opens it. And who should fall out but her greatest enemy, who declares that everything is about to change...
- After the End: The Doctor and companions have to travel here in order to protect what remains of post-CyberWar humanity.
- The Alleged Spaceship: The grav-raft Yaz, Graham, and the other survivors escape in isn't all too reliable, to be polite.
- Blunt "Yes": The Doctor, pointing out to the Lone Cyberman that his emotions put him at odds with what he is, gets the blunt response of "You are correct."
- Call-Back: Two of the devices the Doctor and company bring to try and defend the small group of humans they find are designed to shut off their emotional inhibitors and fill the air with gold particles. Gold was previously noted as the Cybermen's weakness in the classic series and briefly alluded to in "Nightmare in Silver". Ten turned off a Cyberman's emotional inhibitor to destroy it in "The Age of Steel".
- Child Soldiers: Ethan has been trained to fight Cybermen since he was four.
- Cliffhanger: Yaz, Graham, and three of the survivors are trapped on a Cyber Cruiser as Ashad and his reawakened army storm the control room. At Ko Sharmus' planet, the Doctor opens the Boundary to discover it leads to ruined Gallifrey, and the Master reappears through the portal, pompously declaring that everything is about to change.
- Continuity Nod: At the end of the universe, there is a portal to Gallifrey.
- Cool Gate: The Boundary on Ko Sharmus' planet, which is a colourful portal that activates on proximity.
- Doorstop Baby: Brendan is found in a basket on the road, no note or anything else to identify him.
- The Dreaded: Ashad is even this to other Cybers. He makes them scream. Apparently part of the ascension process involves drilling into them, and it's painful.
- The Eeyore: Yedlarmi is cynical enough about their chances of survival that Graham actually outright calls him this at one point.
- G-Rated Drug: Crossing over with I Need a Freaking Drink, but the Doctor has spiked humbugs with ginger, which affects Time Lords like alcohol.
- Happily Adopted: Brendan is gladly adopted by the couple that finds him.
- Hassle-Free Hotwire: A Justified Trope as Ethan has been trained as a Child Soldier to fight Cyber armies from age four, and the Doctor is well, the Doctor.
- Heroic Sacrifice: Ethan attempts to give himself up to spare his friend, but Ashad realizes he's lying and guns down the other one, instead.
- Hypocrisy Nod: Ashad concedes that the same qualities which make him a threat are antithetical to the nature of Cybermen. The Doctor is surprised he's willing to be so introspective.
- Incoming Ham: The Master, who jumps out of the Boundary all smiles!The Master: WOW! Ah! That's a good entrance, right?
- Internal Homage: The scenes of the dormant Cybermen leaving their cells on the Carrier have heavy visual references to similar scenes in "Earthshock". The soldier Cybermen on board the ship even get a costume redesign to make them appear more similar to the 1980s design.
- Oh, Crap!: Graham, Yaz and the humans they're with when they find out that the Cyber Carrier they're on still has an active Cyberman army onboard, and Ashad and his minions are reactivating it.
- OOC Is Serious Business:
- In past episodes, when the companions state the obvious when pointing out that something the Doctor tried didn't work, the Doctor normally responds with mild annoyance. In this episode, when they point out that the Doctor's defenses against the Cybermen didn't work, the Doctor is livid, yelling that she knows, effectively shouting at them to shut up.
- Normally when the Doctor tells the companions to stay back and let her handle a threat alone and then they insist on coming anyway, the Doctor is resigned and lets them come along. In this episode, however, when she tells them to go off with the other humans and they insist on staying with her, she shouts at them to listen to her and to go with the humans because it is far too dangerous for them since they are at risk of being converted into Cybermen.
- The Doctor's usual reaction to a lack of resources would be to make the best of what she's got to hand. Here, she's absolutely furious at the lack of defences until it's pointed out to her that nobody in the settlement is a soldier, just scared civilians trying to survive.
- Party Scattering: When the Cyber drones wipe out the Doctor's makeshift defenses, she sends Ryan, Yaz, and Graham to the escape ship while she attempts to hold the Cybermen off. Yaz and Graham get away with the humans, but Ryan is cut off and rejoins the Doctor.
- Rebellious Spirit: The Doctor mentions having hotwired warp drives while a bored teenager on Gallifrey.
- Redemption Quest: The Doctor was unable to follow Captain Jack's instruction not to let the Lone Cyberman get the Cyberium in the previous episode as human history would have been radically altered or even eliminated in 1816. In order to make up for this as best she can, she and her companions are travelling to the Lone Cyberman's time to stop them on their own turf.
- Running Gag Stumbles: Usually, one of the Fam will state the obvious and the Doctor will reply in a mildly annoyed tone that she gets it, thanks. This time, when her plan has failed and she's staring traumatised at another death, all three do it because they're slightly panicking, she whirls around and screams that she knows.
- Sealed Army in a Can: Yaz, Graham, and the humans who escaped take refuge on a disabled Cyber Cruiser. Then they discover it's a troop transport containing thousands of warrior-class Cybermen.
- Shut Up, Kirk!: Ashad derails the Doctor's "The Reason You Suck" Speech with a Blunt "Yes".
- So Last Season: The Cyber-drones destroy the defences the Doctor and company brought with them to protect the humans, two of which were intended to respectively deactivate the Cybermen's emotional inhibitors and exploit their past allergy to gold.
- So Proud of You: Brendan's mother while preparing him for his job interview and gushing over his picture in a newspaper.
- Spare a Messenger: Ashad decides to spare Ethan so he can tell others of how the Cybermen wiped out humanity. His pontificating on the subject allows the Doctor to get the drop on him with a grenade.
- Special Edition Title: The episode begins with Cyberman debris floating in space; a Cyber head floats towards the camera as we zoom into the eye to begin the intro.
- Title Drop: Ashad says he plans to bring about the "ascension of the Cybermen" while gloating to the Doctor.
- Two Lines, No Waiting: The plot switches between the two groups of characters fleeing the Cybermen, and... an early 20th-century Irish policeman named Brendan, who has some weird things going on about him.
- Unspoken Plan Guarantee: The companions take the time to explain what each of the Doctor's devices is supposed to do and how it will stop the Cybermen. Therefore all of the devices are destroyed by the Cyberdrones without even having a chance to do anything.
- Wham Shot:
- Brendan gets shot and falls off a cliff... yet he suffers no broken bones and the bullet doesn't even penetrate his skin.
- Brendan lives to old age and gracefully retires, gifted with a clock. Waiting outside the building are his adoptive father and the officer who hired him, as old as they were on his first day in the Gardaí. Then they take Brendan to have his memories wiped, with a device that resembles a prototype Chameleon Arch. He doesn't question any of this, which suggests on some level he was expecting it.
- The Boundary, which is supposed to open up to a random part of the universe, leads straight to Gallifrey!
- The Master jumping through the Boundary to the Doctor.
- What the Hell, Hero?: At the beginning, the Doctor is still in soldier mode and the remaining humans call her out on her Lack of Empathy.
- The X of Y: "Ascension of the Cybermen".