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You may be looking for the titular pathogen.

Praxeus was the sixth episode of series 12 of Doctor Who.


What connects strange bird behaviour in the skies above a Madagascan beach to mysterious deaths by a deadly virus that seems to be spreading? And what does a famous British astronaut have to do with all of this? Can the Doctor, Ryan, Graham and Yaz solve this puzzle before it's too late?


Somewhere in space, the spaceship of an astronaut called Adam Lang is malfunctioning. He attempts to try and fix it but it does not work. The capsule starts spinning and turning violently as he tries to deploy the parachute.

Back on Earth in the early 2020s, off-duty police officer Jake Willis tackles a shoplifter to the floor, only to get scolded by a worker called Joyce, who reminds him that he should be on a break.

In Peru, Gabriela Camara takes her friend Jamila Velez to see a river so they can film it, only to find it has been polluted with plastic waste with birds gathering above, despite normally being beautiful. Late that night, Jamila goes outside her tent and is attacked by an unseen force.

Elsewhere, Jake is drinking in a bar as a breaking news story comes on the TV. It states that Adam is now missing, presumed dead. He is devastated until he receives a text from someone claiming to be Adam, telling him to come and find him somewhere in Hong Kong. Meanwhile, Gabriela wakes up, only to find that Jamila is not there anymore. She goes out to find her and comes across a bird dropping out of the sky. As she goes to touch it, Ryan Sinclair appears and stops her, telling her that something is wrong with the birds.

Jake arrives in Hong Kong. He tries to break into a warehouse where Adam supposedly is but fails to do so. Nearby, Yasmin Khan and Graham O'Brien arrive, brandishing a set of skeleton keys and they follow him in.

By a beach in Madagascar, a laboratory worker called Aramu greets his coworker, Suki Cheng. As they settle down for work, they spot the Doctor sprinting down the beach asking for help. Spotting a body in the water, the three work to get him to ground. The Doctor explains that she usually has help from her friends, but "I gave them all errands."

Meanwhile, Gabriela threatens Ryan about Jamila disappearing, but he denies knowledge as something is wrong with the birds. As Gabriela frisks him for weapons, she introduces herself, supposing Ryan knows her already. He admits he does not and she explains she runs a popular travel vlog with Jamila called Two Girls Roaming. Ryan gathers one of the fallen birds for research as Gabriela receives news that there was an ambulance call-out only one mile away that morning.

Inside the warehouse, Jake questions Graham and Yaz, presuming they had come from the European Space Agency, but they are unaware of Adam going missing. Yaz explains they have been told to find out the reason behind some unusual energy readings coming from the building, unaware that a figure in a full hazmat suit is watching them.

On the beach, the Doctor helps the man out of the water and Aramu identifies his uniform as a member of the US Navy. As the three introduce themselves, the Doctor explains that she has been checking for survivors after an American submarine went missing in the Indian Ocean. As they go to move the man inside Aramu and Suki's lab, he wakes up, begging for help. He gives his name as Zach Olson and explains that his sub got hit and was invaded by something before they could react. As he talks, a stone-like crystalline substance grows and spreads from his hand across his body. It eventually reaches his face, completely covering his features before his body shatters into dust. Stunned, the Doctor tells the others not to be alarmed and she laments not being able to see a connection between the three seemingly unrelated events she has sent her friends to uncover.

Ryan and Gabriela arrive at San Pedro hospital, although it appears deserted. Exploring, Ryan finds another dead bird and he ignores Gabriela's warnings to look inside a quarantined area. Inside, they find Jamila lying on a hospital bed with the same stone coverings as Zach had. Ryan uses his comm dot to contact the Doctor as Jamila starts spasming, her eyes blank. As the TARDIS arrives, the Doctor explains that Jamila is already dead but still being attacked, just as she too disintegrates. Ryan fails to calm Gabriela down as the Doctor realises the severity of the situation.

Meanwhile, Graham and Yaz track down the strange energy readings in the warehouse and discover a room full of strange alien consoles. As Yaz investigates, Adam is illuminated, looking very ill and still in his spacesuit, hooked up to the machinery. Jake rushes over and goes to unplug him, but the others stop him for his safety. Yaz uses her comm dot to call the Doctor but Adam warns them to escape just as two hazmat figures appear and start firing at them. Yaz holds up one of the control panels to the figures and they stop shooting. Sensing a chance, they escape, with Jake helping carry Adam out. However, Jake reveals that he is not an active police officer and so he cannot help more. The Doctor materialises and realises the figures and their weapons are not from Earth.

To escape, she leads her friends, Jake, and Adam into the TARDIS, where Ryan and Gabriela are already waiting. With everyone meeting each other, Yaz refuses to join them. She explains that the device that the aliens did not want to shoot must have been important, so she should be left behind for one hour to get it. Although the Doctor initially declines her, Gabriela volunteers to join, so the Doctor begrudgingly lets them explore.

As the TARDIS takes off, the Doctor performs a medical check on Adam. She receives a phone call from Aramu and Suki, letting her know something else unusual has happened. Landing back in Madagascar, the Doctor goes to use the lab. Graham wonders how Jake and Adam know each other; although Jake says they are married, Adam instead says they have split up because Jake did not put in enough effort in their relationship. As Ryan and Aramu discuss the strange birds like the ones in Peru, a very large flock gathers overhead. Ryan mentions to the Doctor about the one he picked up but Graham shouts to them that Adam's condition is getting worse. Aramu decides to keep watch of the birds.

Back in Hong Kong, Yaz admits to also not recognising Gabriela as they find the control panel from earlier. Yaz notices that it is triangulating signals from two other places, one of which is Madagascar. Briefly hiding from one of the hazmat aliens, it uses the control panels to teleport away. Yaz wants to follow it, to Gabriela's bewilderment.

Ryan hands the Doctor the dead bird and she tells him to dissect it. Talking to Suki about the lab, she checks the equipment and tells Graham and Jake to connect Adam to an IV drip, which Graham has experience with. As Suki collects some of the devices the Doctor needs, explaining she is working on a marine filtration system, the Doctor uses Suki's computer to analyse Adam's readings. Turning quiet, she tells the group that Adam has been infected with an alien pathogenic disease and she does not know how to stop it.

Meanwhile, Yaz insists on following the creature through the teleport. Despite not knowing what could happen, they channel the spirit of Two Girls Roaming to do it anyway. In Madagascar, Graham tries to comfort Jake about Adam's situation. Jake explains that he did not show to Adam's launch to the International Space Station seven months ago as he is not good with emotions, commitment, or foreign travel. Jake admits that knowing that his husband is an astronaut, he believes there is no way he could love somebody like him.

Yaz and Gabriela land somewhere dark but safe and celebrate surviving. Yaz believes they have landed in an alien colony while Gabriela spots some machinery that Yaz realises is part of the missing submarine. In the lab, Suki compares the blood of Adam and the bird, with hopes of using it to engineer a virus. However, the rock-like growths are spreading to Adam's face and the current antibiotics are not working. As Graham alerts the group that the birds are intensifying, Ryan notices his bird is full of plastic inside - something Suki notes is not uncommon in ocean areas. The Doctor realises the alien pathogen is attacking the plastic eaten by the birds and controlling them as if it was a living creature. She quickly dismisses Auton interference and wonders how this relates to the crystals appearing on people. She then realises that microplastics are everywhere, unable to be broken down, and are ingested by humans all the time, which is what Suki and Aramu's lab works to prevent. As the Doctor notices the dead bird's natural enzymes fighting back against the alien pathogen, Suki realises they could make a virus out of it.

Calling Yaz on her comm dot, the Doctor fills her in as Yaz explains where she has landed. However, the Doctor has an epiphany about Suki and her lab being suspiciously over-prepared. Suki says that the Doctor has helped give her more answers than when she experimented on Adam and, naming the infection as Praxeus, she calls it relentless and teleports away. As the birds intensify, the group go to escape, but they are attacked inside. The Doctor retrieves the samples and they all barely escape to the TARDIS waiting outside, although Aramu is unable to follow.

The Doctor locks on to Yaz's comm dot signal to join her but worries about the virus being spread by birds. Adam insists the potential cure should be tested on him but Jake tries to talk him out of it. Meanwhile, Yaz finds a dead hazmat alien and removes its mask to find out it has been fully infected by Praxeus as well. The Doctor uses the antidote on Adam under the promise that the TARDIS will make more if it works. She, Graham, and Ryan leave Jake and Adam inside.

Meeting up with Yaz and Gabriela again, the Doctor reveals they are not on an alien planet, but on an alien-made base deep under the Indian Ocean. They are beneath a natural pollution gyre, which is where Praxeus multiplies best. Ryan questions how it could arrive on Earth at all and the Doctor decides to track down Suki. Inside the TARDIS, Adam promises Jake that, if he dies, he should stop dodging life. Finding a hazmat alien, the Doctor believes it has not disintegrated due to having different biology to humans and wonders if they were experimenting on Adam to find a cure as well. Meanwhile, Adam's life signs turn vital.

Exploring the tunnel, the Doctor's group uncovers the end of a spaceship from which Suki emerges with a gun. She reveals that the hazmat aliens were members of her crew and she is not from Earth either; her planet was ruined by Praxeus so her people were sent off to find an antidote. She found Earth as the perfect lab to test in, although they crash-landed, destroying the ship and spreading the virus further. However, she brags at having found a cure that she has used on herself, although the Doctor reminds her it was made for humans. Inside the capsule, the Doctor tries to bargain with Suki, but Suki finally succumbs to Praxeus and disintegrates.

Outside, the Doctor assembles her friends to find an antidote and they are joined by Jake and a fully-recovered Adam - the TARDIS having worked and distributed a cure. Inside the shuttle, everyone works on the ship, setting its autopilot to the stratosphere with the organic fuel cells loaded with the antidote that will disperse across the world. However, it will also send the Indian Ocean crashing into their base, forcing them out.

Running back to the TARDIS, the shuttle's autopilot fails, but the Doctor knows it will at least take off. As the TARDIS flies away, Adam realises Jake is missing and he arrives on-screen, acting as a manual pilot for the ship. With no other choice, the Doctor gives him his instructions to release the antidote and eventually does it successfully, ridding the Earth of the virus. However, the ship breaks up in space and the Doctor laments being unable to save him as he proves his dedication to Adam. However, as she says it, the TARDIS materialises around Jake, landing him safely inside, and the husbands kiss.

Returning to Madagascar, the Doctor and friends bid a fond farewell to Jake and Adam, telling them to look after the planet. Jake jokes that he deserves a statue for saving humanity and Adam suggests that they hold their honeymoon on Madagascar. Gabriela decides to join them so she can vlog about it and the two groups part ways, safe in the knowledge that no matter how separate they are, the seven billion lives of Earth are safe.


Uncredited cast[]

  • Hazmat Alien - Jamie McKee[1]


General production staff

Script department

Camera and lighting department

Art department

Costume department

Make-up and prosthetics



General post-production staff

Special and visual effects


South Africa crew
General production staff

Art department

Camera and lighting department


Not every person who worked on this adventure was credited. The absence of a credit for a position doesn't necessarily mean the job wasn't required. The information above is based solely on observations of the actual end credits of the episodes as broadcast, and does not relay information from IMDB or other sources.



The Doctor[]

  • The Doctor indicates she has more than one brain.
  • The Doctor gives the team gold stars.
  • The Doctor describes herself as "a romantic".






  • The Doctor mentions the Autons when speculating about the infected birds.
  • The aliens use hazmat suits.

Medical injuries and ailments[]

  • The Doctor does an MOT on Adam.
  • Praxeus is transferred to humans through contact with infected birds.
  • The Doctor informs Adam Lang that his bloodstream has been infected with an alien pathogen.



Story notes[]

  • This episode had Doctor Who 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 the episode was filmed around January and February 2020.[2]
  • The Doctor's opening monologue places Praxeus as taking place "early in the third decade of the 21st century."
  • This story marked the first television role in any licensed Doctor Who media given to a Brazilian actress, Gabriela Toloi.
  • This story marked the last time Millennium FX worked on an episode of the show.[3]
  • Soyuz spacecrafts, like the one seen in the story, exist in the real world.[4]
  • An early version of the story was titled Hush, in which Jake would still have been a serving policeman while Suki's colleague was called Sanya, both working at a port where the Doctor was alerted to a beached submarine used to investigate plastic pollution. The virus would have infected humans into becoming 'plastic people' who would be revealed as clones trying to cure Adam due to Sanya's efforts at finding a cure to the Hush virus through the manipulation of Earth. (DWM 570 supplement)
  • The script for Praxeus names the hospital visited by Ryan and Gabriela as Cusco Hospital.[5]


  • 3.97 million (BBC overnight)[6]
  • 5.22 million (BBC overall)[7]


  • The Sea Devils were going to return. This was proven false.

Filming locations[]

(All DWM 570 supplement)

Production errors[]

If you'd like to talk about narrative problems with this story — like plot holes and things that seem to contradict other stories — please go to this episode's discontinuity discussion.
  • As the Doctor is standing in the TARDIS doorway watching Yaz and Gabriela leave, it is obvious that the interior of the TARDIS is just a photo pasted onto the back wall.


Home video releases[]

DVD and Blu-ray releases[]

  • This story was released as part of the Complete Twelfth Series boxset on DVD and Blu-ray in region 1/A on 9 June 2020, in region 2/B on 4 May 2020 and in region 4/B on 3 June 2020.

Digital releases[]

  • In the United Kingdom, this story is available on BBC iPlayer.

External links[]