Doctor: Jodie Whittaker
Bradley Walsh (Graham O'Brien)
Tosin Cole (Ryan Sinclair)
Mandip Gill (Yasmin Khan)
Warren Brown – Jake Willis
Matthew McNulty – Adam Lang
Joana Borja – Gabriela Camara
Molly Harris – Suki Cheng
Gabriela Toloi – Jamila Velez
Soo Drauet – Joyce
Tristan de Beer – Zach Olsen
Thapelo Maropefela – Aramu
Directed by Jamie Magnus Stone
Written by Pete McTighe, Chris Chibnall
Script editor: Fiona McAllister
Produced by Nikki Wilson
Executive producer(s) Chris Chibnall, Matt Strevens
Incidental music composer: Segun Akinola
Length: 49 minutes
First broadcast 2 February 2020
The Doctor and her companions, joined by ex-police officer Jake, video blogger Gabriela, and medical researchers Suki and Amaru, investigate a new bacterium infecting people in Peru, Hong Kong, and Madagascar. Those infected become covered by a crystalline substance before their bodies disintegrate. Birds in the local areas have also started acting aggressively towards humans.
The group finds Adam, Jake’s husband and an astronaut, is infected and held in a Hong Kong lab. While rescuing him, they are attacked by humanoids in biohazard suits. Yaz and Gabriela remain behind to investigate further while the rest go to Suki’s Madagascar lab via TARDIS to study Adam. Yaz and Gabriela see another humanoid use a panel to teleport somewhere and follow him, ending up in an alien-looking place.
The Doctor determines that the bacterium is drawn to microplastics that have saturated living beings, and that the birds’ natural enzymes are trying to fight it, causing them to become violent. As she generates an antidote, she realizes Suki’s lab is perfectly equipped for this task, and Suki reveals she is one of the remnants of an alien race ravaged by Praxeus, their name for the bacterium. When Yaz informs the Doctor of their discovery, Suki teleports away. After the birds kill Amaru on the beach and burst into the lab, the Doctor and the others flee to the TARDIS and subsequently to Yaz’s location. Adam volunteers as a test subject for the antidote, and the Doctor programs the TARDIS to synthesize more, should it be successful.
When they arrive, the Doctor determines they are at the bottom of the sea in a shell of plastic made from the Indian Ocean garbage patch. They find Suki aboard her ship and learn that her kind came to Earth, rich in plastics, to study Praxeus and create their own antidote. When Suki demands the antidote from the Doctor, she is told that it will only work on humans. Suki’s body, infected by Praxeus, is soon consumed and disintegrates. The Doctor finds that the ship runs on organic fuel, and with Adam successfully cured, has her allies load the batch of antidote into the ship and sets it on course to explode in the atmosphere to distribute it via the jet stream. The autopilot fails, however, and Jake stays behind to pilot the ship on its course, while the others retreat to the TARDIS. The Doctor uses the TARDIS to rescue Jake in the millisecond before the ship's destruction. With the cure successfully spread, the Doctor drops Jake, Adam, and Gabriela off, and Ryan suggests they travel the world together.