Lions once hunted mammoths in Canada. Dire wolves stalked mastodon in Germany. And as recently as 1,300 years ago, a coyote-sized cat called the Eurasian lynx brought down deer in Great Britain. But the lynx, and all those other big predators, got out-hunted—and in some cases hunted out—by an even better predator: humans.

Now, though, the lynx are coming back. Not on their own, of course. If all goes according to plan, British and Scottish conservationists say that by the end of 2015 they'll put the lynx back where it belongs, at the center of the British isle's food web. "At the moment, Great Britain's forest ecosystems are broken," says Paul O'Donoghue, the lead ecologist with Lynx UK Trust, the group in charge the effort. "The lynx is the best tool to add some balance to the forest ecosystem." To do that, O'Donoghue's team will undertake a process called "rewinding." They'll find lynx in other parts of the world, make sure they're OK to move, and bring them to their new homes. It's difficult and controversial, but if researchers are right, it's also fantastically important.

Apex predators do a lot to keep an ecosystem together. For one, they keep lower predators and herbivores in check, so they don't overbreed and decimate plant life...which in turn cascades into human civilizations. Ecologists have been able to trace events—through sometimes complicated linkages—like Lyme disease outbreaks, agriculture pest flare-ups, and even increased flooding to the absence of apex predators.

Bring those predators back, though, and an ecosystem can swing back to health. At least, that's the idea.

The Eurasian lynx still roams wild in most of Europe, and all the way across Russia. O'Donoghue's cats will come from eastern Europe. "These are the exact same species that used to live in the UK," he says. This is the first order of business when rewilding: making sure that the predator is a good fit in its once and future home. This isn't just to prevent obvious blunders—you wouldn't put modern, African lions into the Canadian tundra. "We have to make sure we're returning an animal to its historic natural range, some place where it makes sense ecologically," says William Ripple, an ecologist at Oregon State University whose expertise was crucial in the 1990s reintroduction of wolves back into Yellowstone.

Lynx UK Trust is eyeing three privately-owned, intact, and relatively underdeveloped forests for rewilding—two in England, one in Scotland. Finding the right habitat isn't just a matter of grabbing up a bunch of green acreage. The quality of the forest matters. This means doing detailed analyses, not just mapping the forest's extent, but also calculating the value of what's available. For example, you could have a millions of available acres, but they'd be completely useless in a strip a hundred yards wide. Likewise, lynx won't do well in a forest that is fragmented by housing developments, farmland, or roads.

Next comes food. "We’ve picked areas that have particularly high deer densities and where the lynx will have high impact," says O'Donoghue. Great Britain is plump with prey, but after an initial chow-down (hopefully) brings the herds down to manageable numbers, will the deer continue to be a sustainable food source for the lynx? It's possible they won't. And if newly reintroduced lynx go hunting for other food, farmers and livestock owners are concerned they'll choose other local fare—a flock of sheep, perhaps. Ranchers in the American West blame grey wolves, originally released in Yellowstone, for killing cattle—though their culpability is hard to prove. Not many people catch a wolf in the act, and with only a mangled carcass as evidence it's hard to tell if the perps were wolves or coyotes. O'Donoghue's solution is to take things slow. He and his team will reintroduce just four to six lynx in each forest. Only after monitoring the ecosystems for three to five years will they decide whether it's ready for more. "The point is to make the whole process driven by facts and data," says O'Donoghue.

But that does't mean they won't check in with the neighbors before they start releasing wild cats. The Lynx UK Trust is polling the communities around each forest—in at least one of the areas the idea enjoys 80 percent support. These polls are crucial for getting government approval on the reintroduction project, and also important for the survival of the cats. "If there is an attitude of tolerance, the chances of a successful outcome are higher," says Ripple. "Intolerance results in persecution." He's speaking from experience here. In the American west, the wolves's endangered species status is under constant assault by ranchers, cattlemen, and other people who feel like their rural territory is being encroached upon. Similarly, the most vocal opponents of the UK lynx reintroduction have been cattle and livestock owners, who don't buy O'Donoghue's assurances that there will be more than enough deer to keep the lynx sated. So just in case, O'Donoghue says, "We'll run a full compensation program, so no farmer will suffer any loss whatsoever."

Once the researchers get all that out of the way, the really hard part starts: actually moving lynxes. They'll come from established lynx populations in eastern Europe via a quarantine facility before boarding a plane to Great Britain. Once the pathogen-free kitties arrive on the island nation, they'll spend four to five weeks in a fenced-in, wooded enclosure getting fattened up on fresh meat and eased out of the anxiety of the big migration. "By the time they are released, these will be some of the healthiest lynx around," says O'Donoghue. No word if that health care will be covered by the NHS.

And how will they know if the rewilding works? Ecologists will watch populations of lynx and deer, of course, as well as concomittant stats in the rest of the ecosystem. With GPS collars, they'll monitor each lynx's territory size and habitat use. But if the project succeeds and the lynx take hold, the weird call of a deposed apex predator, returned to the throne, could sound out for the first time since before the Picts and the Gaels formed the Kingdom of Scotland.