Susan Fleming was working in the garden one evening when she heard the call.
It came from the darkening hills that bordered her rural property in Uxbridge, Ont.
And sent a shiver down her spine.
"It was just like a baby being killed but also a donkey screaming," she recalls. "It was just the most bizarre thing."
She ended up spending her evenings outside, keening an ear for that haunting sound. The creature that prowled those hills didn't disappoint, sending its strange siren into the night again and again.
"You don't forget when you hear the sound, because it's half howl, half yip. It's really unique."
Consumed by curiosity, Fleming wasted no time in sounding out the scientific community.
And she learned it was the call of the coywolf.
"What we think of as coyotes in this part of the world is really a coyote-wolf hybrid," she told The Huffington Post Canada. "It's a new species. That's a pretty remarkable thing."
Even more surprising, this predator has been living in our midst for decades -- thanks to the social savviness of its coyote ancestry, which allows it to virtually vanish in urban environments.
"They have the remarkable ability to operate under the radar," Fleming notes.
"We're not talking about a raccoon or something small. This is a large animal. Most people have no idea they're there."
Indeed, the coywolf has only been around for the past 100 or so years, but has begun infiltrating cities only very recently.
Fleming, an accomplished filmmaker, heeded the call.
Debuting Feb. 14 on CBC, her new film, "Meet the Coywolf," traces the footfalls of this elusive animal from the cradle of coywolf civilization near Ontario's Algonquin Park to our very doorsteps.
That's where things get really interesting.
Coywolves are flourishing in major cities, as these medium-sized carnivores devour everything from rats to rubbish to Canada Geese.
At one point during filming, Fleming spotted a coywolf skulking off with someone's discarded turkey. And then there's the fascinating interplay between coywolves and their urban playgrounds.
When fire trucks howl near Toronto's High Park, the coywolf population answers, lending their own inimitable call to the chorus.
But coywolves are raising another kind of alarm. With their big, strong jaws, flourishing numbers and increasing ease in urban locales, should humans be afraid of the big bad coywolf?
If you believe some media accounts, certainly. The Toronto Star's Carola Vyhnak writes about this urban scourge "plaguing" the Greater Toronto Area.
She cites thousands in damages caused by these apparently ravenous beasts, which mulched through at least 545 animals back in 2008.
And certainly, their smaller relative, the coyote, has had an increasingly uneasy relationship with humans.
"Over the last 30 years or so, there has been a general escalation of seriousness in encounters between people and coyotes," Erich Muntz, a supervisor at Cape Breton Highlands National Park, says in the film.
"Through the '90s, there were a number of incidents where coyotes were following people, and chasing them.'
In 2009, budding folk musician Taylor Mitchell was killed on Cape Breton's Skyline Trail. It was the first known fatal attack by a coyote on a human.
When it comes to the coywolf, however, Susan Fleming isn't pushing panic buttons. After all, these masters of disguise seem to have long learned the wiles of big city living, padding softly beneath our very noses. And feasting on our excesses.
"There's a lot of garbage in the city," Fleming says. "There's just so much food available.
"One of the things that came up again and again with the scientists is that they're still going about their business the same way they always have. The thing that changes them is when we change."
It's the story of that fine balance between human and hybrid that propels Fleming's mesmerizing glimpse of the not-so-wild kingdom on our doorstep.
And she thinks this story is only beginning.
"It's a fascinating story to watch over the next 10 years."