On Earth, New Year’s Day 2019, a long-buried creature is beginning to stir. The most dangerous creature in the universe and it will stop at nothing to claim the Earth. Conquest in 9376 rels.
The Doctor must gather all her friends and resources to prevent another invasion. And if they fail… The Daleks are coming.
In the 9th century, a creature attacks the Earth. Three tribes of people come together to destroy it. After many deaths, they succeed and cut it into three pieces. The Three Custodians transport them to three distinct places around the world: Anuta Island, Siberia, and Yorkshire. The third Custodian in England attempts to take his piece to Yorkshire but is killed en route by thieves, shot from his horse while in Sheffield. The man’s final fragment remains unguarded for over 1000 years.
It is New Year’s Day in 2019 Sheffield. Two archaeologists, Lin and Mitch, gather around a proper archaeological find that they have helped uncover underground, both pleased to have something to do on the usually quiet New Year’s Day. Mitch hesitantly brings up the topic of a kiss that the two shared at a party the night before, with both eventually confirming that it did mean something to them. Lin explains that that was the reason why she suggested they come in and the two promise to make plans later before Lin notices something odd near the hand of the skeleton they are studying. Later, Mitch bags up the mysterious object and explains his excitement over how their find could be key to uncovering the mysteries behind the supposed Battle of Hope Valley. The two go off to talk. Meanwhile, the current Custodians on Anuta Island and in Siberia notice something strange happening with their shrines and the bagged object in Sheffield begins to expand and writhe.
In the TARDIS, the Thirteenth Doctor, Graham, Yaz, and Ryan watch some “cosmic fireworks” out of the door. The four discuss which of the nineteen New Year’s Eve celebrations they have visited is their favorite (Graham choosing the original celebrations in Mesopotamia, Ryan choosing Sydney in 2000, and Yaz choosing 1801, discovering a dwarf planet with Giuseppe Piazzi), but before the Doctor can set off their twentieth on Quantifier, an alarm sounds, signaling trouble on Earth. The Doctor explains that a terrible group of non-terrestrial things is attempting to teleport together, towards none other than Sheffield.
At the dig site, a tentacle that was held in the bag has pushed itself off the table. Lin and Mitch initially attribute it to rats before Lin discovers a huge tentacled creature stuck to the wall and nearly touches it before the TARDIS dematerializes. As the Doctor and her friends introduce themselves and the excavators explain the situation, the creature is revealed to have disappeared into the water and the Doctor collects some residue to scan. Yaz leads everyone out as the area is placed under quarantine and the group returns to the TARDIS. Lin and Mitch go their separate ways, promising to meet up again, but Lin begins to act strangely as she sits down in her car.
With the TARDIS scanning for any extraterrestrial life, they land back in Graham and Ryan’s house, needing some household ingredients to help with analyzing the residue. While they are there, the doorbell rings and Graham immediately shuts the door on the visitor without talking to them. As they continue ringing, Ryan answers instead, leading a man into the house – his father, Aaron. However, despite his attempts to be kind, the Doctor does not return the gesture because of him being missing from Ryan’s life and not showing to Grace’s funeral. Ryan begrudgingly agrees to go and grab a coffee with him, but not before Graham also tells Aaron some choice words.
Meanwhile, in Lin’s house, she returns to go to the bathroom, taking off her jacket to reveal that the creature is settled on her back with one tentacle inserted on her neck. It begins to talk, gloating at being able to control her fully, and eventually starts talking through her mouth. In the TARDIS, the Doctor finally founds out what creature they are dealing with: a Dalek. Controlling Lin, the Dalek mutant forces her to access UNIT’s archives so it can learn about Earth’s capabilities and fulfill its purpose. The Doctor continues to explain the background of the Daleks to Graham and Yaz and wonders how it is able to move so fast when it is out of its casing. It is revealed that the Dalek’s control of Lin has now extended to forcing her to drive her car at over 100 miles per hour and she is quickly pulled over by police. Relishing the opportunity, the Dalek mutant grabs a policeman, leaving him presumably dead, as Lin steals his uniform and speeds away in the police car.
In the café, Aaron attempts to sell a combo microwave and oven to the owner to no success. To Ryan, he admits that his new business venture is not working very well and may have to return to the offshore oil rigs before he asks Ryan how he is. Ryan is very angry at his attempt to start their rehabilitation in that way and explains how lonely, abandoned, and lost in life he has felt without his father’s presence. The severity of the situation dawns on Aaron and he explains how he made some bad decisions in the past that forced him to run away because he was too scared to face the truth but promises not to hide anymore.
Outside in Sheffield, Mitch talks to Yaz on the phone about what he has seen and the TARDIS materializes next to him, having followed his phone signal, and Yaz ushers him inside. After the initial shock subsides, the Doctor plans to scan for any other traces of the Dalek, but after mentioning the Custodians, they return to Graham and Ryan’s house. While there, Mitch unloads his findings and explains the history of the battle, with the Doctor realizing that the Dalek was revived thanks to being placed under ultraviolet light. After Yaz explains that she cannot get hold of Lin at all, Mitch and the Doctor begin to worry about her and return to the TARDIS. The Doctor is able to identify the coordinates of both Lin and the Dalek and discover that they overlap.
Meanwhile, Ryan and Aaron return home, and Ryan enters the TARDIS, where he tucks his father’s microwave away. Attempting to get a read on the Dalek, the TARDIS’ systems short-circuit thanks to interference from the creature. The Doctor explains that should be impossible unless it is a reconnaissance scout, a specially advanced form of Dalek that was one of the first to leave Skaro and reach Earth. The Doctor sends an annoyed Graham off to buy some peanut butter to fix her systems.
Still controlling Lin, the Dalek speeds to the MDZ Research security archives in Yorkshire and promptly kills the only security guard, using him to unlock a secure room and retrieve a Dalek gun. She suddenly stops, hearing the Doctor’s voice in her head, speaking from the TARDIS. The Dalek confirms that it is a recon scout and it now has a weapon to try and conquer Earth. The Dalek attempts to laugh at her and, enraged, the Doctor summons a hologram of Lin so they can see each other. Getting through to Lin for a short time, she shows her how Mitch is safe and they are coming for her, before revealing to the Dalek that she has bought time to reboot her systems. Promising to find the Dalek, the TARDIS takes off, leaving Graham and Aaron alone in the house together.
Flying after the Dalek, Mitch explains that MDZ is a weapons research company that buys alien weaponry from the black market. The Dalek prevents the TARDIS’ bio-fix, so the Doctor goes “old-school”, tracking CCTV cameras, GPS and car number plates until the Dalek shoots the cameras out. Taking Yaz’s phone, the Doctor resolves to get help. However, attempting to phone Kate Stewart at UNIT, the Doctor is instead put through to the ‘UK Security Helpline’, where the call center worker, Polly, eventually learns that UNIT has been suspended following financial disputes. Powerless, the Doctor hangs up. Back in Graham’s house, Graham brings down a large box full of a child’s drawings and toys. They are revealed to all be Aaron’s, and Grace kept them all her life. Aaron states that he wishes to be better at life, and Graham tells him there is still time to make it up.
Lin, still being controlled, drives up to a farm workshop, and after shooting the owner, states that “I shall be reborn” before collecting a lot of metal parts. Lin is forced to start welding many plates together and as she begins to tire, she attempts to fight against the creature. As she does so, the Doctor, Yaz, Ryan, and Mitch run to find her. By the time they do, the Dalek mutant has already disconnected from her, leaving her weak but alive. The Doctor tells her friends to return her to the TARDIS while she has a personal talk with her enemy. Finally, the fully-built Dalek emerges. It is not perfect, is clearly made out of recycled metal from memory, and has a claw arm. The Doctor sonics its laser as it syncs itself up, allowing them to talk. The Dalek claims it has control over the Earth and will summon its fleet to take over the planet, but the Doctor contests it, stating that she is not human. The Doctor finally identifies herself to the Dalek and it overrides the block from the sonic screwdriver to shoot at her. She ducks away, but the Dalek states that it has all the information it needs and will conquer Earth in 9,376 rels, before taking off through the ceiling.
Back in the TARDIS, the Doctor explains to her friends that she did the opposite of getting rid of the Dalek and sets the TARDIS in flight. As Lin admits she is still feeling shaky, the Doctor gives her some medication before she receives a phone call. It is Graham, asking where she has gone. The TARDIS returns to pick him up, allowing Aaron to witness it materializing, and the two enter.
The Dalek lands in a barren area, quickly followed by the army. They surround it, guns all pointed, but refuse to listen to the Dalek’s time period for surrender and they begin to get killed. Their bullets are harmless to the Dalek and in response, some of its domes open up to reveal guided rockets that finish off the rest of the soldiers, running away. After shooting down a tank as well, the Dalek flies off. In the TARDIS, Aaron’s microwave slides across the floor and he explains about it. After talking to Ryan about his life with the Doctor and realizing that the Dalek is made of metal, the two take apart the microwave to remove its element. As more and more alarms sound, the Doctor realizes that the Dalek is moving to the center of British communications.
The Dalek bursts through the ceiling of the General Communications Headquarters, immediately killing the security guard, and diverts all possible power towards Skaro. The Doctor discovers that it has shut down the UK’s Wi-Fi, phone signals, and internet to power the transmission as one family laments being forced to talk to each other. The TARDIS lands in GCHQ and although the Dalek immediately attempts to exterminate the Doctor, it is deflected by the TARDIS’ shield. The rest of the group emerge and the Dalek refuses its “final, final, final warning”, causing the Doctor to enact her plan. Telling the Dalek that Earth is protected, this year and every other, the Doctor slides around the room behind the Dalek in one direction while the others run the opposite way. Working together to turn the Dalek around, they attach the microwave parts to its casing and, with the voltage and amperage fluctuating wildly, it burns through the recycled metal case and causes a small explosion. With the signal to Skaro not having sent, the Doctor celebrates, but not for long as it is revealed that the mutant has now taken over Aaron. The Doctor promises to send the creature to its fleet as long as it keeps Aaron alive.
They enter the TARDIS, with the Doctor stating that they have reached the fleet, but opens the doors to see a supernova, with a vacuum corridor ready to drag the mutant into space from Aaron’s back. However, the corridor expands, beginning to take Aaron with it. As he barely holds on by the doors, Ryan risks everything to run and grab him, finally saying that he forgives him and loves him, and with the two holding hands, the Dalek mutant is finally jettisoned into space. The TARDIS doors finally close with the threat removed.
Sometime later, the TARDIS lands back at the underground dig site in Sheffield, returning Lin and Mitch to their work with everything back to normal. The Doctor offers a trip in the TARDIS to Aaron, but he politely turns it down, with Ryan promising to call him when he returns. With Team TARDIS back together and safe, they prepare to head back into the box – destination everywhere.