"Praxeus" is the fifth story of Season Thirty Eight (New Series 12) and was written by Pete McTighe and Chris Chibnall, and directed by Jamie Magnus Stone.
Pete McTighe wrote the previous season story "Kerblam!".
Jamie Magnus Stone directed the stories in the first recording block of this season which included this story and the first part of the opening story "Spyfall". He also directed "Ascension of the Cybermen/The Timeless Children" - the final two-part story of this season.
This story marked the first television role in any licensed Doctor Who media given to a Brazilian actress, Gabriela Toloi.
Parts of this story were filmed in South Africa along with "Spyfall".
The Doctor and her three travelling companions, Graham O'Brien, Ryan Sinclair and Yasmin Khan, are investigating three separate distress signals received by the TARDIS (see the end of the previous story "Fugitive of the Judoon"). The Doctor has travelled to Madagascar and sent Graham and Yasmin to Hong Kong. While Ryan has been sent to Peru.
According to Gabriela, Peru has the most beautiful river in the world but they discover it has been polluted with rubbish.
The Doctor's opening monologue places this story as taking place ‘early in the third decade of the 21st century’.
The Doctor and her three travelling companions keep in contact with each other using Comm Dots. In the 2018 story "The Tsuranga Conundrum" the Tsuranga crew used Comm Dots to communicate over great distances.
Yasmin and Graham have a set of skeleton keys that they use at the warehouse in Hong Kong. Jake wonders if they are from Interpol or ESA.
The Doctor indicates she has more than one brain and describes herself as ‘a romantic’.
Zach Olson, the US naval officer who is washed up on a beach in Madagascar, is from a US submarine that went missing in the Indian Ocean. Before dying he tells The Doctor that he tried to rescue his entire navy team before he succumbed to the virus.
Gabriela and Jamila are vloggers on the channel Two Girls Roaming. At the end of this story Jake and Adam go on their honeymoon at last, with Gabriela following. She wants to vlog about it, which Graham suggests calling Three Idiots Roaming.
The Doctor informs Adam Lang that his bloodstream has been infected with an alien pathogen. A pathogen is a microorganism that carries disease.
The Doctor discovers that the Praxeus virus is transferred to humans through contact with infected birds. The Doctor discovers though that the bird enzymes are trying to fight back Praxeus.
This story had fans pointing out the parallels between the fictional bacteria Praxeus and the real-world Coronavirus. The real virus was discovered in December 2019 and spread in 2020, notably after this story was filmed and initially during the week that this story was broadcast – creating a strange coincidence.
The Doctor briefly entertains the possibility that the Autons might have taken over the world's discarded plastic. In fact, the Nestene Consciousness recently did take over the North Atlantic garbage patch, with ongoing plans for world domination through Bakin Petrochemicals. Rhys Williams took care of this threat in the short term in the Torchwood audio story "Sargasso".
When the TARDIS materialises around Jake, he appears in the interior. This has been seen before (see "Bad Wolf/The Parting of the Ways", "Dinosaurs on a Spaceship" and "Let's Kill Hitler").
Gabriela asks if the TARDIS is an optical illusion, while Jake believes the interior of the TARDIS is a building.
The TARDIS has a holographic screen that can be extended away from the console it also has a bioreading table that The Doctor uses to synthesise the Praxeus antidote.
After using the teleport device Yasmin thinks she has found an alien colony which The Doctor reveals to just be an alien construct. Yasmin is relieved that she and Gabriela didn't teleport into an active volcano.
Astronaut Adam Lang is onboard a Soyuz spacecraft while calling Control. The spaceship suffers automatic system failure with a failed DMP, unable to switch to ballistic descent and maintain trajectory. Soyuz spacecrafts, as the one seen in this story, exist in the real world.
Adam Lang is heard to state that while in orbit he enjoyed watching Earth from above, seeing hurricanes and the aurora borealis, and the turn of the planet.
Suki and Aramu are working on a marine filtration system connected into a Crystal Oceans Initiative; Microversion. In Suki’s lab there is a broad-spectrum antibiotics, a high-power microscope, blood cultures, rapid genome sequencing, a spectrophotometer, and a super-fast incubator.
The Doctor uses a Chemical Analyser on Suki's computer to check the chemical data on Adam's Blood Analysis.
The climatic moment of the story, where The Doctor desperately saves Jake Willis from certain death in the exploding spacecraft after he sacrifices himself to destroy Praxeus, made fans recall the climatic death scene of former companion Adric in the 1982 story "Earthshock" in which the Fifth Doctor was unable to save Adric due to the Cyber-Leader damaging the control console of the TARDIS, resulting in Adric plummeting towards Earth, being the reason the dinosaurs becoming extinct.
This story contains an error - as The Doctor is standing in the TARDIS doorway, watching Yasmin and Gabriela leave, it is obvious that the interior of the TARDIS is just a photo pasted onto the back wall.