Merle Davis spent a December afternoon baking chocolate-chip cookies with rosemary sprigs for her fellow organizers with the Mining Injustice Solidarity Network.

She was hosting the group's holiday party that night. And although the network hopes to change the world through the power of protest, its core still fits comfortably in the cozy living room of her rented house.

But the festivities had an undertone of suspicion. Two people had recently joined the group, telling its grad-school-aged organizers that they hoped to "grow as a couple" through a new-found commitment to dissent. "Kat" was the shy, soft-spoken one, and in her late 20s, maybe early 30s. "Alex" was buff and boisterous, in his late 30s, maybe early 40s.

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The activists say that as the autumn turned to winter, the newcomers seemed increasingly focused on one question: How were the protests for July's Pan Am Games shaping up?

Suspicions had been aroused by the time of the party, where Kat spent an hour making small talk about her life before she ducked into a bathroom. When she did, Ms. Davis, 25, grabbed a pen and piece of scrap paper for a fellow activist. He wanted to jot down everything Kat had just said in hopes of checking out the details.

No one in the group drew any conclusions that night, but Ms. Davis lay awake wondering. "I think that was the night it kind of dawned on me there was a cop in my house," she says. "And there is this person, misrepresenting themselves."

Authorities will neither confirm nor deny they ran undercover infiltrators ahead of the Pan Am Games. Police "will not comment on investigative tools or procedures," Sergeant Kristine Rae, a spokeswoman for the Ontario Provincial Police unit tasked with Pan Am security, said.

Within weeks of the party, the MISN members were convinced they had been duped. In February, they kicked "Kat and Alex" out after confronting them in a café and asking them if they were undercover officers. They denied it, but they have not been seen in activist circles since.

In recent weeks, The Globe and Mail has reached out via Gmail and Facebook, knocked on doors and tried to find people who know Kat or Alex. But they have not surfaced to tell their side of the story.

Eager recruits

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The intelligence powers of government officers – consider Toronto's "carding" practices or Ottawa's recent passage of new spying legislation – are hot-button issues, but they pale beside a controversy that erupted five years ago.

In June, 2010, the G20 summit weekend in Toronto went awry. On the Saturday, a mob smashed storefront windows and set ablaze police cars that had been abandoned as dozens of rioters carved a path of destruction downtown. On the Sunday, police pulled off the kid gloves and pulled down their Plexiglas face shields and geared up for melees and mass arrests. Watchdogs and observers spent years asking why authorities suddenly lurched between seeming passivity and running amok.

Now comes the Pan Am Games, an event that will cost taxpayers $2.5-billion, nearly 10 per cent of that total for security. Police have to keep tabs on more than 6,000 athletes at 61 venues with room for more than a million ticket holders. Last year, the OPP carved out a "JIG" – a joint intelligence group – to explore the likelihood of threats such as terrorism and protests. Weekly briefings began last September.

Toronto's anti-mining protesters say they first saw Kat that month. They were holding a memorial for a Guatemalan activist. She introduced herself, and said she wanted to learn more. They invited her to join.

In early November, Kat and the man she called her boyfriend, Alex, attended an orientation session at Intergalactic Coffee in downtown Toronto's west end. "They were very eager to get involved," recalls Kate Klein, one of the organizers. "I remember thinking, 'Oh, these two are going to be a handful. They seemed very, very new.' "

Over the next few months, the group's organizers went from being welcoming to being wary. They started taking notes and using their phones to keep records of their interactions, some of which they later shared with The Globe and Mail.

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The activists say their intent was to establish whether they were, in fact, being watched. Their suspicion of government spying flows from what happens in repressive states. "When I've done solidarity work in Guatemala, I have personally witnessed activists being followed by strange vehicles for days at a time," organizer Rachel Small says.

The group frequently cites industry figures that indicate three-quarters of the world's mining companies are headquartered in Canada. They say this means Canadian citizens must keep the corporations accountable.

So when Toronto-based multinational Barrick Gold Corp. said it would donate enough metal for 4,000 gold, silver and bronze medallions for the Pan Am Games, MISN members started talking seriously about protesting.

And they were not alone.

Activists in Toronto for a variety of causes often march together under a broad banner of anti-globalization. MISN had talks last fall about joining forces on Pan Am protests with groups such as the confrontational anti-capitalists at the Ontario Coalition Against Poverty, and the immigration-policy activists at No One Is Illegal.

These discussions piqued Alex's interest, MISN members say. They recall him asking: "OCAP uses violent tactics – do we use tactics like that?"

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He grew so fixated on nailing down plans for Pan Am protests that Ms. Klein sat him down last fall for a "goals versus tactics 101" lecture.

"I put my foot down and said: 'we're not there yet,' " she recalls, explaining that the group was then only talking about what it could achieve.

Now that the Games are here, the anti-mining activists say they hope to be "spoilsports and smear leaders" who pop up at random events. MISN's website asks followers to dress in referee jerseys and "emote horror, disgust, rage at the spectacle."

Pan Am protests began in earnest during Wednesday morning's rush hour, with a demonstration led by No One Is Illegal that jammed traffic in the Financial District and coincided with a climate summit of world leaders.

The protesters' raucous rhetoric and the heavy presence of uniformed police had suggested an ugly showdown loomed – yet the crowd of about 150 dispersed after blocking intersections for an hour. Police made no move to arrest or search anyone and their leaders seemed to be urging restraint. The Globe has a copy of the Pan Am policing handbook. Page 68 reminds officers, in bold type, about Section 8 of the Charter of Rights and Freedoms: "Everyone the right to be secure against unreasonable search and seizure."

Even so, no law prevents police planners from trying to find out how trouble might arise in the weeks, months or even years before a major event.

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The chase

A stare-down in a subway station followed the MISN holiday party.

After Kat and Alex left a meeting, Ms. Klein texted her boyfriend, Terrance Luscombe, to let him know. He decided to follow the couple.

A 28-year-old law student with "Resist" tattooed on his forearm, Mr. Luscombe is not formally a member of MISN. But he was the one who jotted down his conversation with Kat at the holiday party. "I wanted to keep track of this because I had gone through this," he says.

Mr. Luscombe was arrested before the G20 and jailed for 20 days. Hours before the rioting, police took 17 suspected protest leaders into custody on "counselling to commit mischief" charges. Six were convicted, but the charges against Mr. Luscombe and 10 others did not stick.

Courts later revealed two undercover officers had passed themselves off as activists named "Khalid" and "Brenda." They had been tasked by a police joint-intelligence group to spend more than a year infiltrating protest groups.

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Mr. Luscombe – who had known Khalid – says his brush with the law was not wasted. As a defendant, he got thousands of pages of disclosure about police techniques. He kept this in mind as he followed Kat and Alex to the Christie subway station that day in January.

"If they were following the same game plan, they would be meeting a handler," he remembers thinking.

Inside the station, he went down the wrong staircase and found himself staring right at Kat and Alex – and vice versa. "That was such an awkward moment."

He doubled back and scrambled out of the station. He says he saw two police cars roll up.

Later, Kat used Facebook to contact an MISN organizer she trusted.

"Alex said he thought someone was hiding in the stairwell watching us and he ran away," her message said.

She said she had recognized Mr. Luscombe. "I'm really uneasy about it," she said. "I just wanted to see what you know about him …"

Before long, it would be time to clear the air.

Faceless on Facebook

Some things can be unequivocally said about Kat and Alex. They are relative latecomers to Facebook, starting their accounts within days of each other in late 2013. They named each other in their relationship status. They "liked" Ontario groups involved in anarchism, environmentalism and aboriginal rights.

They appear never to have posted photos that show their faces on Facebook. Kat's profile picture is a word cloud featuring "Freedom," "Justice" and "Equality." Alex opted for the stylized Guy Fawkes mask that is the symbol of anonymous agitators everywhere.

E-mails from The Globe to active Gmail accounts that MISN members said the pair used were not returned. Facebook friend requests got no response. The activists say Kat and Alex gave no phone numbers.

Public record searches turned up no contact information. Nor did queries related to the couple's reputed career choices. "He said he worked in landscaping for a buddy, very freelance, and she was self-employed as a dog walker," Ms. Klein recalls.

The Globe contacted two dozen dog walkers, but none could say who Kat was.

A few people in one park said she looked familiar, and did walk a dog, or dogs.

Kat had told MISN members she once lived in an apartment on Regina Street in Waterloo, Ont. Door-knocking in that neighbourhood turned up no leads. It's a small street with a half-dozen high-rises.

The Globe is not publishing the full names used by the couple because it has not been able to verify them.

Alex has a somewhat uncommon surname, but several people with the same family name did not seem to know him. Social media indicate he was a fan of the A.S. Roma soccer team. The president of the Toronto fan club said he was not a member.

Their Facebook pages have not been updated in months.

'Are you cops?'

In February, MISN's organizers invited Kat and Alex to a café off Bloor Street called El Cafecito. It was time to be frank.

The couple wanted to know why they had been deemed untrustworthy. "We've been in your home," Alex said at one point. "I don't know why you don't trust us," Kat said at another.

They expressed anger that Mr. Luscombe was present.

MISN members said they had asked him to monitor the meeting, but Kat accused him of taping everything with his cellphone.

Which he was.

MISN member: Are you cops … ?

Alex: No! No.

Kat: No.

Alex: I think we're done.

MISN: Yeah. Okay, well you're no longer MISN members, and we do not want to have any contact with you in the future.

Alex: Great.

Members of the group have not seen or spoken to Kat or Alex since.

With reports from Stephanie Chambers, Madeline Smith and Verity Stevenson.

With reports from Stephanie Chambers, Madeline Smith and Verity Stevenson