You've probably heard the rumours before now. Everyone without the clearance level to know better wants to get their dig in. "Did you hear it's a capture/kill mission for Bigfoot? Are we gonna capture and contain Mothman next? What about BatBoy? Are the Navy chasing Champ around Lake Champlain?"

Yes. It's true – we're sending you out there to deal with a particularly aggressive Bigfoot.

I'm sure you've snickered. Don't worry. Contrary to rumours, we don't actually assign Army Rangers to this sort of duty for finding something humorous. Quite the opposite in fact.

You think Bigfoot is funny because we want you to think Bigfoot is funny. We've bankrolled Hollywood comedies and farcical documentaries, paid off men in gorilla suits, perpetrated hoaxes with bear prints and goat fur, bribed and brainwashed cartoonists to get especially silly depictions on children's television. Even the term "Bigfoot" comes from us, planted in the media in 1958, a term people would find even harder to take seriously than "Sasquatch".

Why? We'll get to that later.

You've read the briefing documents and I'm sure you're aware of the news reports. The slaughtered animals; the missing hikers; those children who just vanish while walking ahead of their parents on the trails in National Parks. Our efforts to portray them in the media as particularly smart chimps aren't entirely accurate either. They aren't chimp-level smart. They're smarter. To be precise, they are exactly as smart as us.

So, what do we actually know? Quite a lot it transpires. Several think tanks located out in the desert managed to decipher some sort of broadcast we picked up about a decade ago. Some sort of quantum-level thing – something to do with tachyons as I understand, I don't have all the details but as far as we can tell the apes we call Sasquatch evolved alongside us. We walked in the daytime; they walked in the night-time, our nocturnal siblings in the shadows. But while we were still wandering hunter-gatherers, they…changed. Like we would a few thousand years later. Tools. Weapons. Agriculture. Domesticated animals. Stable settlements. As humanity blinked in the Pleistocene sun, Sasquatch's population exploded across the night. They blanketed the planet in the tens of billions.

They made things that we still can't comprehend, even though we've thoroughly studied the surviving pieces we discovered by accident in shadowy hangers out in Area 51. Organic technology. They made trees and birds of prey grow into fast-moving ships, herds of animals that became trains, bushes that became flying vehicles. From insects and pigeons they made things equivalent to cell phones, televisions, computers. Atomic bombs. The broadcast described vast shining cities, stretching across glaciers and penetrating the deepest caverns, grown bio-ships of ivory and spider-silk, creatures tending them with hundreds of blinking eyes.

We were rare, like gorillas now, a few hundred thousand left at best. We avoided their settlements just like wild animals today avoid ours. Sasquatch understood we were intelligent like them, but avoided us just as we avoided them, saw us as fairies, as gnomes, ascribed us supernatural powers, and probably said we ate bad children while they slept in daylight. They fenced off our dwindling wild populations in conservatories, outlawed poaching but in the underground consumed our bones as aphrodisiacs.

Then their civilization fell. And we did it.

This is where the story gets muddy. Maybe some trickster forest god showed humanity favour, showed us the master's tools and how to use them. Maybe we got lucky finding a piece of their tech lying around that we could interpret. Why we did it, we don't know. Perhaps they hunted us, perhaps we were simply afraid. Perhaps it was just that they fenced us in, unintentionally or not. We simply don't know what the truth is. Maybe those old tales from the Native cultures about wars with the Hairy Man were more truth than myth. Somehow we acquired their technology, and with it, we instigated a dominance shift in which humanity became the dominant species of Earth.

We wiped out 70% of Sasquatch's population in a single day. The Day of Flowers, the Hidatsa called it. Supposedly every flower bloomed that day, while our enemies died in their sleep. Then we hunted the rest down. But we went further than just killing them. With a few of the more twisted of their devices, we drove the survivors mad, even those hiding beyond our reach. We trapped them in their own minds, blocking higher functions and leaving their bodies to fend for themselves like any ordinary ape. We slaughtered their living machines and burned their vast shining cities with bioweapons that reduced everything to slurry and dust that washed or blew away in spring rain and wind.

We left no traces. Not even our own memory. We turned one of the weapons on ourselves, wiped out any knowledge of Sasquatch and the greatest civilization the planet had ever seen. Only a few humans protected themselves from the effect, kept the forbidden knowledge, just in case and it became the folklore that has been passed down through the years. The rest of us went back to being hunter-gatherers, living in caves and struggling to create fires, none the wiser.

Which brings us to today.

You've heard about the bear attacks on camps. Those random disappearances that I mentioned before. The encounters being reported on podcasts and YouTube videos. The vocalisation recordings. The Sasquatch are somehow regaining their forgotten intelligence and knowledge. Maybe it's something to do with the eruption of Mount St. Helens back in the 80's. Maybe they never truly lost it. We don't know. This is why the ever-increasing number of "Bigfoot sightings" is so worrying. Why the attempts at contact, however indecipherable, are even more of a concern.

Yes. Sasquatch are just like us. That's what makes them so dangerous. We wiped them from history and memory. We dissolved their civilization and we slaughtered most of their species. Just ask yourselves: If they got the chance, what would they do to us?

Oh, and one final thing. If you see one charging you – aim for the head and empty your clip into it. It might buy you a few seconds.