Scavenging on an alien junkyard planet, the Doctor (Jodie Whittaker) and her friends Graham (Bradley Walsh), Yasmin (Mandip Gill) and Ryan (Tosin Cole) are caught in the detonation of a sonic mine. They wake up aboard the Tsuranga, an entirely automated ship heading for a medical space station.
The Doctor meets some other patients—Eve Cicero (Susanne Packer), her brother Durkas (Ben Bailey-Smith), their synth robot Ronan (David Shields), and Yoss (Jack Shalloo), a pregnant man. The Doctor and head nurse Astos (Brett Goldstein) notice something heading for the ship. An alien entity gains access to the ship and begins to damage the escape pods. Astos is trapped in a pod and dies when it explodes.
Aided by Astos’ colleague Mabli (Lois Chimimba), the Doctor learns that the alien entity is a Pting, which eats non-organic material and is highly dangerous. If the space station they are headed for detects it, the authorities there will destroy the ship. The Doctor tries to stop this while Yasmin and Ronan try to keep the ship’s power source away from the Pting.
Ryan and Graham try to help Yoss as he enters labour. The Doctor, Eve, and Durkas try to gain manual control of the ship. The Doctor learns that Eve has a critical heart condition that will kill her if she interfaces with the ship, but she sacrifices herself to navigate through an asteroid field. When she dies, Durkas takes her place.
The Doctor realises that the Pting is simply looking for its food-energy sources. She takes a failsafe bomb and feeds it to the Pting before jettisoning it into space. Durkas brings the Tsuranga to the space station and Yoss gives birth successfully. The Doctor joins Mabli and the patients in honouring Eve for her sacrifice.
The episode was written by executive producer Chris Chibnall and directed by Australian Jennifer Perrott. It received mixed reviews. The Pting was created by writer Tim Price. Throughout the episode, Ronan never blinks. When his leader dies, Ronan will shut down, as Samurai warriors did when their leader suicided. If not, they would become wandering Ronin.
The strongest threat level recognized by the ship’s computer is Chalice, or Calice in Canadian French profanity. In Doctor Who lore, Pilot’s Heart Disease is common among Neuro Pilots in the 67th Century. It could be controlled by increasingly powerful adrenaline blockers. This was a Base Under Siege episode, which has been around since the Second Doctor. The Pting is rather too cute to be threatening. It’s not the best episode, frankly.