The Doctor (Jody Whittaker) and her companions, Graham (Bradley Walsh), Ryan (Tosin Cole), and Yaz (Mandip Gill), are joined by an ex-cop named Jake (Warren Brown), a video blogger named Gabriela (Joana Borja), and a couple of medical researchers named Suki (Molly Harris) and Amaru (Thapelo Maropefela) to investigate a new strain of bacteria infecting people in Peru, Hong Kong, and Madagascar. The infected are covered in grey scales and then explode. At the same time, birds in the area start to attack humans.
They learn that Jake’s husband astronaut Adam Lang (Matthew McNulty) is infected in a Hong Kong lab. Trying to rescue him, they are attacked by humanoid aliens in hazmat suits. Yaz and Gabriela investigate further while the others go to Suki’s lab in Madagascar to study Adam. Yaz and Gabriela witness another humanoid using a panel to teleport somewhere and they follow him to an alien place.
The Doctor learns that the bacterium is attracted to microplastics that have saturated living creatures, and the birds’ natural enzymes, trying to fight the infection, make them aggressive. Working on an antidote, Suki reveals that she is a remnant of an alien race decimated by Praxeus, as they call it. Yaz informs the Doctor and Suki teleports away. The birds kill Amaru on the beach and burst into the lab. The Doctor and the others use the TARDIS to reach Yaz’s location. Adam volunteers as a test subject and the Doctor programs the TARDIS to synthesize more antidote.
At the bottom of the sea, in a shell of plastic made from the Indian Ocean Garbage Patch, they find Suki, who reveals that her species came to Earth to study our abundant plastic garbage, so they might create an antidote to Praxeus. It turns out the TARDIS-synthesized antidote only works on humans and she dies of the disease. The ship runs on organic fuel and Adam, now cured, loads the antidote on the ship and sets it to explode in the atmosphere, distributing the antidote. When the autopilot fails, he sacrifices himself to pilot the ship. But the Doctor is able to rescue him with the TARDIS milliseconds before the explosion. The Doctor drops off Jake, Adam, and Gabriela.
The episode was written by Pete McTighe and Chris Chibnall and directed by Jamie Magnus Stone. It received mixed reviews. It was filmed in Capetown, South Africa with the Spyfall episodes. It has been pointed out that the Praxeus virus behaves quite a bit like like Coronavirus. The background is the worldwide proliferation of plastic, which sounds like an alien plague to me.