Honestly, if you grew up watching the David Tennant era, you probably have a very specific, slightly uncomfortable memory of humanoid felines in nun habits. They weren't just background fluff. The Doctor Who cat people, known formally as the Sisters of Plenitude, represent one of the show's most successful—and deeply disturbing—makeup effects. They first padded onto our screens in the 2006 episode New Earth. Since then, they've become a sort of shorthand for the "New Who" aesthetic: a mix of high-concept sci-fi and body horror hidden behind a friendly face.
They're weird.
That's the best way to describe them. They have these flat, prosthetic faces that manage to look both serene and predatory at the same time. While the show has featured other feline-adjacent species, like the Cheetah People from the 1989 serial Survival, the Sisters of Plenitude hit different. They were sophisticated. They were medical "miracle workers." And, as the Tenth Doctor eventually discovered, they were hiding a secret so unethical it makes most Cybermen plots look like a playground dispute.
The Sisters of Plenitude and the Ethics of New Earth
When the Doctor and Rose Tyler land on New Earth in the year 5,000,000,023, they find a society that has seemingly conquered every disease known to man. At the heart of this medical utopia is Ward 26. The Sisters of Plenitude, a religious order of cat-like humanoids, run the hospital with terrifying efficiency. They can cure anything. Cancer, petrifold regression, the flesh-eating virus—you name it, they fix it with a simple spray or an injection.
But how?
The answer is "The Flesh." No, not the doppelgangers from the Matt Smith era (though the naming overlap is a bit confusing for casual fans). In New Earth, the Sisters grew thousands of artificial humans in pods. These weren't just empty shells; they were living, breathing people born with every disease in history so the Sisters could study the cures in real-time. It’s a classic Doctor Who moral dilemma. Is the survival of a million citizens worth the forced suffering of a "manufactured" few? The Doctor's answer, as usual, was a resounding "no."
He was furious. You can see it in Tennant’s performance—the way his jaw sets when he realizes these "nuns" are actually biological farmers. It's one of those moments where the show stops being a fun space adventure and starts asking some really uncomfortable questions about the cost of progress.
The Evolution of Novice Hame
You can't talk about Doctor Who cat people without talking about Novice Hame. Played by Anna Hope, Hame is the emotional anchor for the species. In New Earth, she’s a complicit antagonist, blinded by her devotion to the order and the Face of Boe. She’s essentially a zealot.
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By the time we see her again in Gridlock, she’s changed.
It’s been years for her. She’s spent decades tending to the Face of Boe in the dark, crumbling under-city of New New York. The makeup reflects this, too. In New Earth, the prosthetics are pristine and sleek. In Gridlock, Hame looks weathered. She’s older. Her fur is thinner in places. She has spent her life in penance for the sins of the Sisters. This kind of character growth is rare for a "monster of the week" species, and it’s why Hame remains a fan favorite. She’s a reminder that in the Whoniverse, redemption is always on the table, even if you started your career as a murderous feline nun.
Why the Makeup Design Actually Worked
Back in 2005 and 2006, the BBC's budget wasn't exactly "Marvel movie" level. They had to be smart. Millennium FX, the legendary prosthetics team behind most of the modern era's creatures, handled the Doctor Who cat people. They didn't go for a full-face mask that would muffle the actor's voice or kill the performance. Instead, they used a "sculpted" approach that left the mouth and eyes relatively free.
This allowed the actors to emote. You could see the flick of a whisker or the curl of a lip. It made the Sisters feel like a real species rather than guys in rubber suits.
- The Hair Work: Each prosthetic piece was covered in hand-punched hair to give it a realistic texture.
- The Eyes: The use of subtle contact lenses gave them that predatory, reflective "tapetum lucidum" look without looking like a cartoon.
- The Costumes: The habits were intentional. They contrasted the animalistic nature of the species with a sense of rigid, religious discipline.
It’s a design philosophy that holds up even today. If you go back and watch New Earth in HD, the cats look better than many of the CGI creatures from a decade later. There’s a weight to them. A physical presence.
The Connection to the Face of Boe
One of the most persistent questions in the fandom involves the relationship between the cat people and the Face of Boe. Why were they his primary caretakers? The show never gives a 100% explicit answer, but it’s hinted that their species has a long-standing tradition of service and medical expertise that predates the New Earth colony.
Some fans theorize that the cats were "uplifted" or genetically modified by humans during the Great Expansion. It makes sense. Humans love cats. If we were heading out into the stars and needed a companion species to help us run things, we’d probably pick felines.
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However, the more interesting angle is the religious one. The Sisters of Plenitude weren't just doctors; they were a sisterhood. Their devotion to the Face of Boe—who we eventually learn is likely a very old, very evolved Captain Jack Harkness—adds a layer of irony to the whole thing. They are worshipping an immortal man while torturing "disposable" humans to find the secret to immortality.
Other Feline Species in the Whoniverse
While the Sisters of Plenitude are the heavy hitters, they aren't the only ones. We have to look at the broader history of Doctor Who cat people to see the patterns.
- The Cheetah People: Featured in the final story of the original run, Survival. These were much more feral. They hunted on a dying planet and could "infect" humans, turning them into cats. It was a very 80s take on lycanthropy.
- The Tharils: Seen in Warrior's Gate (1981). These were lion-like beings who could move through time. They were highly sophisticated but had been enslaved by humans.
- The Cat-Humans of the Future: By the time we get to the Year 5 Billion, it seems like the line between "human" and "animal" has blurred significantly.
The Sisters of Plenitude represent the "refined" version of this trope. They aren't monsters because of their claws or their teeth; they’re monsters because of their bureaucratic coldness. They represent the horror of "efficiency" over empathy.
Fact-Checking the "Cat People" Myths
There's a lot of misinformation floating around on Reddit and various wikis about these characters. Let’s clear some of it up.
Myth: The cat people are related to the Judoon.
Nope. No relation. The Judoon are rhino-based mercenaries from a completely different part of the galaxy. The cat people of New Earth are a localized species (or at least localized to that era of human expansion).
Myth: There was a planned spin-off.
Sort of. During the height of the "Whoniverse" expansion (when Torchwood and The Sarah Jane Adventures were launching), there were rumors of a show set on New Earth. It never happened. Probably for the best—the makeup budget alone would have bankrupted the BBC.
Myth: They use CGI for the faces.
Hardly ever. In the 2006-2007 episodes, it was almost entirely practical prosthetics. Any CGI was used for wide shots or environmental effects. This is a big reason why the Doctor Who cat people felt so grounded.
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Practical Takeaways for Fans and Writers
If you’re a fan looking to dive deeper, or maybe a writer interested in how Doctor Who builds its worlds, there are a few things to keep in mind regarding this species.
Look at the Subtext
The cat people aren't just "cat people." They are a commentary on the Victorian "Angel in the House" trope turned on its head. They look soft and caring, which makes their callousness toward "The Flesh" even more impactful. When designing or analyzing sci-fi species, look for that contrast.
Watch "Gridlock" for the Nuance
If you only remember the Sisters as villains, go back and watch Season 3, Episode 3. Novice Hame’s arc is one of the best examples of a minor character getting a soul. It’s also where we get the final payoff for the Face of Boe’s storyline.
Understand the Limitations
Prosthetics are hard. The actors behind the cat masks, including Anna Hope and Adjoa Andoh (who played Sister Jabe in a different episode but is a staple of the era), had to work twice as hard to convey emotion. Notice how they use their head tilts and hand gestures to compensate for the lack of facial mobility.
The Doctor Who cat people are a perfect example of why the show works. It takes something familiar—a house cat, a nun—and twists it into something that feels both alien and uncomfortably human. They aren't just monsters to be defeated; they are a mirror held up to our own ethics, asking us exactly what we're willing to sacrifice for a longer life. Next time you see a ginger tabby, just hope it doesn't start talking to you about "the latest medical advancements."
To explore more of this era, check out the behind-the-scenes features on the Series 2 and Series 3 DVD sets. They go into incredible detail about how the Millennium FX team sculpted the different "breeds" of cat people seen in the background of the New York Senate. Seeing the sheer variety of feline designs they came up with—from Persians to Siamese influences—really highlights the craftsmanship that went into making New Earth feel like a living, breathing world.