It sounds like the tagline for the world's lamest horror movie: Just when you thought it was safe to go back to your spin class...

But last week, a single fitness studio in Hamilton, Ontario, was linked to more than 72 positive cases of COVID-19, with an additional 2,500 people potentially exposed. What's shocking is that the gym seemingly did almost everything right: six-foot distancing, 50 percent capacity, screening customers, a robust sanitizing regime. "This is not about how well the gym was run; this is about how COVID spreads," Colin Furness, an infection control epidemiologist at the University of Toronto, explained to The Spec. "If you let people hangout together, without masks, sharing air, in the same space for a prolonged period of time ... this was going to happen anyways."

Just look at Europe, where the World Health Organization is reporting "exponential increases" in cases, and warns that the daily death toll could balloon to five times what it was during the peak in April. It appears that the spike there, too, is linked to increased indoor activity — like the Hamilton spin studio outbreak, but on a macro scale. For the moment, the United States has a brief respite from being the rest of the world's cautionary tale about what not to do during a pandemic, but the message we're receiving from overseas is abundantly clear: it isn't safe yet to go back indoors.

After the initial explosion of cases in Europe in February and March, as the disease was still emerging globally, the continent appeared to get the crisis mostly under control by the late spring and early summer. Germany's Bundesliga soccer league even resumed in mid-May with only minor hiccups, making it the first professional sport to return after the pandemic shutdowns. As U.S. cases began to rise again over the summer, foreign correspondents' accounts of life across the Atlantic sounded like dispatches from the moon: "People are out everywhere," NPR's Paris correspondent, Eleanor Beardsley, said in July. "There's a very relaxed feeling that it's — if it's not completely behind us, it's almost behind us."

Famous last words? This week, France recorded 120,000 new COVID-19 cases over the past seven days, "one of the highest rates in the world" according to The New York Times; officials warned that in Paris, hospital beds could reach 70 to 90 percent capacity by the end of October. "We are on the brink of disaster," immunologist Paweł Grzesiowski, of Poland, told The Guardian, despite the fact that the country had managed to stay relatively healthy up to this point. Italy, meanwhile, reported this week its largest one-day total of cases, "with more than 7,300 — easily surpassing the terrible heights the country reached in March," NPR reports. And the reason for the spike across the continent seems to be linked to the casual easing back indoors.

Europe's strict restrictions in the spring took less than a month to visibly downturn the continent's daily confirmed COVID-19 cases, but ever since regional lockdowns began to lift around May 5, there has been a slow — but increasingly steep — rise again. "In several European countries," The New York Times explains, "lockdowns were lifted abruptly, sowing complacency among people who felt they could return to their normal lives." Indeed, as the government in the Netherlands succinctly put it, "In recent weeks coronavirus has had too many opportunities to spread again." Especially as the weather starts to get colder, an already-blasé population might not feel the need to be as diligent as they once were, bringing behaviors that might have been relatively safe outside, indoors.

Take something as simple as mask wearing, the one major and proven precaution notably missing during the Hamilton spin studio outbreak as well. In the Netherlands, where cases have nearly doubled this week, officials had been de-emphasizing masks, fearing they might result in a false sense of security; and yet "the aversion to masks, experts say, could help explain why the Netherlands is suffering such a serious spike, despite being wealthy and well-organized, with one of the best health care systems in the world," The New York Times reports. We know also, from watching countries like South Korea, which never had lockdowns, that part of their success is due to their universal mask wearing and avoidance of crowds. In the U.S. and Europe, though, reopening indoor restaurants and bars, where masks can't be worn all the time, seems to be a contributing factor. New York City, for example, had mirrored Europe in getting its outbreak under control locally, only to have seen renewed spikes since indoor dining got the green light.

Today, the United States sits at a crossroads. To be sure, things here definitely aren't good; they're just not as bad as in Europe at the moment. But cases are rising again, and no one wants us to be back in the position Europe is facing now, with renewed lockdowns and imposed curfews. Instead of letting it ever get to that point, we should prepare for the fact that people who were avoiding indoor activities throughout the summer, thanks to the warm-weather alternatives, could find themselves in the coming days and weeks lured into spaces with the potential to become super-spreading sites as it gets colder.

As Bloomberg argues, extending prohibitions on certain activities — "indoor restaurant dining and drinking," for example — could keep us from snowballing past having any freedoms at all again. And if our government doesn't take measures to protect us, it falls on our own shoulders to weigh the risks that come with gathering inside. After all, just because you're allowed back in the ocean doesn't mean the man-eating great white shark that was in there is gone.

When it comes to spreading COVID-19, no spin class is worth it.