The Thirteenth Doctor

Ryan Sinclair is trying to ride a bicycle with his grandmother Grace and her husband Graham O'Brien, on a hillside in Sheffield. Ryan struggles because of his dyspraxia, and falls off the bike. Frustrated, he throws the bicycle over a cliff and into a wood below. Grace and Graham try to comfort Ryan, though insist that he collects the bicycle, to try again another time, while they head off to the train station. As Ryan ventures to retrieve the bicycle, he sees some strange glowing golden lines suspended in the air. Curious as to what they are he taps one of them and a purple coloured, plant-like pod emerges. Ryan decide to call the police, receiving help from PC Yasmin Khan, an old school friend.

Yasmin at first presumes Ryan is just pulling a prank but Ryan remarks that he can't even touch the pod, as it is freezing. Yasmin touches it but finds it burns her hand. Bewildered, she continues questioning Ryan. Meanwhile, Grace and Graham are riding in a train carriage with a man named Karl when there is a disturbance which causes the train to come to a screeching halt. They find that the other passengers have fled the train. When they try to do the same they find that the doors are locked. They then find themselves trapped by an encroaching floating orb of writhing tentacles and electricity. Scared they call Ryan who rushes to the scene with Yasmin.

Graham orders Grace and Karl to the back of the carriage. Then before the creature can reach them, they are temporarily saved as The Doctor comes crashing down through the ceiling of the carriage and electrocutes the creature with a metal pipe. The orb then departs after hitting everyone with an energy bolt.

Graham O'Brien

With the danger over Karl leaves the train. The others decide to stay as The Doctor questions them about the creature. While doing so she discovers the orb implanted DNA destroying bombs into each of them, and they are liable to explode at any time. Ryan then mentions about the pod that he found earlier in the woods, which Yasmin agrees to take the group to. However, when they get there, they find it has disappeared. Initially unbeknown to The Doctor it has been taken to a warehouse and is being watched over by a person called Rahul who took the pod from the woods as he connected it with the disappearance of his sister. Suddenly the pod becomes active, breaking open and exploding all of Rahul's cameras. Arming himself with a crowbar Rahul witnesses a large, biomechanical creature emerge from the broken pod. Rahul demands to know about his sister, who had previously gone missing but the alien creature kills him by freezing his face.

Meanwhile The Doctor tasks the others to find out if any strange alien activity has taken place recently. While Yasmin checks with her police station and Graham asks some of his bus driver friends, Grace and Ryan take The Doctor back home. While Ryan checks on social media, Grace notices The Doctor's body coursing with and exhaling regeneration energy, intriguing them both. Concerned Grace checks The Doctor's pulse and is surprised to find two instead of one.

Ryan Sinclair

On waking up The Doctor reformats Ryan's phone, and uses it to track the source of the disruption which leads them to the warehouse where Rahul had been killed by the creature from the pod. They arrive on the scene as the alien creature flees, The Doctor and Yasmin chase after it but lose it in the mist. The other's find Rahul's body in the warehouse and The Doctor notices the absence of one of his teeth. Ryan then spots the empty pod and The Doctor inspects it, identifying it as a transport pod. Yasmin and Ryan go to investigate the warehouse and in a small room they discover files of various missing people and a video on Rahul's computer.

After examining the pod The Doctor decides to build herself a new sonic screwdriver from spare parts. While gathering materials from around the warehouse and the transport pod, The Doctor tells Graham and Grace about her experiences with regeneration before proceeding to construct her new screwdriver. When she finishes, Ryan and Yasmin show them Rahul's video in which he talks about his sister Asha's disappearance and his desire to find out the truth in the knowledge that it may kill him.

Scanning the pod again The Doctor discovers a recall circuit. She also deuces that the alien from the train and the pod are at war and are looking to fight on Earth. Graham then gets a call from his friend Kevin, who has information about the alien's whereabouts. The group then depart the warehouse and intercept the orb creature. The Doctor nullifies it and, on scanning it with her sonic screwdriver, she identifies it as a mass of biological data-gathering coils which collects and correlates information. She checks the data it has collected, all of it information about Karl from the train. The second alien, who killed Rahul in the warehouse, then arrives. It reveals itself as a Stenza warrior called Tzim-Sha (mispronounced as 'Tim Shaw' by The Doctor). Tzim-Sha has been sent to Earth on a hunt to seek out a randomly selected human without technology or assistance to bring him back home. However, The Doctor deduces Tzim-Sha has secretly sent the Gathering Coils ahead in advance and thus has broken the rules. On removing his mask Tzim-Sha reveals his face implanted with his victim's teeth. The Doctor is furious and demands that Tzim-Sha leaves the planet. Tzim-Sha ignores this, collecting the data of his target, Karl, who they met on the train earlier, from the coils before teleporting away to hunt down Karl, leaving The Doctor very frustrated.

Yasmin Khan

Chasing Tzim-Sha to a construction yard, where Karl is a crane operator, The Doctor discovers the orb creature part way up the crane that Karl is operating from the control cabin at the top. The Doctor sends Graham and Grace to evacuate the site while she, Yasmin and Ryan make for the top of a second crane to save Karl from the Stenza which is climbing up Karl's crane forcing him to leave the control cabin and crawl along the arm of the crane.

When the trio make it to the top of the second crane The Doctor orchestrates a plan in which Yasmin and Ryan move the crane arm around to meet Karl's crane so he can jump across. But before he has a chance to do so Tzim-Sha captures Karl. The Doctor takes a running jump over to the other crane instead to confront Tzim-Sha. The Doctor, recalling her identity, orders Tzim-Sha to leave him, or face losing the pod's recall device and being stranded on Earth. Tzim-Sha detonates the DNA bombs, but The Doctor reveals that she transferred the bombs into the coils, which were then unwittingly self-implanted into Tzim-Sha when he downloaded the data. The Doctor then thrusts the recall device at Tzim-Sha and Karl kicks him off the crane as he teleports away - much to The Doctor's anger.

Meanwhile Grace and Ryan successfully destroy the orb creature, by electrocuting it with power from the construction site's electrical mains. But the kickback from the electricity shocks Grace and throws her from the crane, severely injuring her. Knowing her injuries are too severe she tells Graham not to be afraid and dies just as The Doctor, Yasmin and Ryan arrive, leaving Ryan and Graham grief-stricken.

During Grace's funeral Graham gives a heartfelt speech. Afterwards The Doctor decides to go and look for her TARDIS, when Yasmin suggests that she change her clothes first. With a new outfit selected, The Doctor returns to the warehouse and, using the remains of Tzim-Sha's technology, she lashes up a rudimentary teleport that will track the TARDIS' trail of Artron energy. As she prepares to leave she says her goodbyes to Graham, Ryan and Yasmin but inadvertently teleports all four of them instead. But instead of finding the TARDIS The Doctor is shocked to see her friends floating behind her all of them suspended and stranded in deep space.