Doctor Who has encountered the Cybermen for almost 50 years, slapping those silver monsters all the way round the galaxy. There's just one problem: we are all Cybermen.
We're not just talking about Danny the cyber-converted boyfriend. Cybermen have proved remarkably good at predicting our own future as a species – and make us ask some very awkward questions about the technology we use every day.
Science fiction author Simon Guerrier and scientist Dr Marek Kukula are Doctor Who superfans, and have tracked the ways science and technology have wormed their way into the sci-fi series in their book The Science of Doctor Who.
For them, Who isn't really about finding and catching the universal bad guys – it's about finding out about ourselves.
Speaking at the Radio Times Festival, Dr Kukula explains, "The original idea of the Cybermen in the 60s came out of thinking about how we might send people into space. Perhaps instead of building spaceships that recreate earth environments, we should just adapt people’s bodies so they could survive in a space environment without a space suit?
"But now, of course, cybernetics is a real science, a real technology. Many of the people around you are benefiting from it. People have robot arms, pacemakers, all sorts of implants. We are becoming genuine Cybermen."
But our connection to the Cybermen isn't just about medical implants, adds Guerrier. "We are far more comfortable with computer systems and making them part of our lives," he points out.
"Even if you don’t have an implant, you might have an app on your phone that monitors your body, how many steps you do.
"We’re also worried about 'deindividuation'." This, Guerrier explains, is a psychological concept that tries to explain why people do things as part of a group that they would never do alone, or act without anticipating the consequences.
"You see it on social media,"says Guerrier. "Because you feel anonymous and remote, you become much angrier, much more aggressive than in real life.
"It’s the same with driving: people who are quite meek in ordinary life. When you put them behind the wheel they become monsters. That’s what Cybermen are. You put somebody in a metal box, they all look the same, and suddenly they do things they never would have dreamed of doing."
Not bad for a children's show.
"It’s a mistake to think that because it’s a show for families that it’s not sophisticated," Kukula explains. "It’s one of the most sophisticated shows on TV, because the format means you can do anything, talk about anything. And although you have to make it palatable for kids, you can add layer upon layer of all this clever stuff."
Few Doctor Who monsters have proved as adaptable – and therefore terrifying – as the Cybermen.
"Cybermen have become a very adaptable fictional concept, because they can reflect our concerns as we develop," Kukula says. "Nobody is concerned about people being made into living spacesuits now, but we are worried about medical technology, how much we can really replace of ourselves, and still be us."