ZHDANOVICHI, Belarus — Members of the Wagner Group, a shadowy Russian mercenary force linked to an associate of President Vladimir V. Putin, have left their traces around the world. They fought in support of pro-Russian separatists in Eastern Ukraine; helped tilt Syria’s civil war in favor of President Bashar al-Assad and fought on the side of a Kremlin-backed warlord in Libya.
At the end of July, they popped up at the most unlikely place yet — an austere Soviet-era sanitarium on a lake outside the sleepy capital of Belarus, a Russian ally entirely bereft of warring militias, armed checkpoints and other markers of the civil wars that usually attract Russian mercenaries.
The beefy Russian men, 32 in all, were noticed almost as soon as they checked in, taking rooms on the second floor of a concrete bloc in a distant corner of the resort and health spa.
In contrast to other Russian clients, they kept to themselves, showing little interest in a late-night disco, which immediately struck the D.J., Veronika Step, as strange. Two of them stopped by the disco to take a look but quickly left, she said.
The men, recalled Ms. Step, were so unsociable that she and fellow female workers started joking that perhaps they should call the police “to find out what is wrong with them.”
What unfolded next, however, was even stranger: a heavily armed special unit of Belarus’s top security agency, still called the K.G.B., stormed the resort late at night, dragging the Russians away in handcuffs.
Shortly after that, Belarusian state television shared video footage of the raid, showing a number of tattooed, heavyset Russians lying face down on beds and on the floor in boxer briefs at the resort. Taken away in unmarked vans to a police station, they were forced to kneel facing a wall for 22 hours, according to their interview with the Russian state-run media.
President Aleksandr G. Lukashenko of Belarus, who was facing a presidential election in less than two weeks, convened an emergency meeting of his top security officials, saying that the Russians were mercenaries with “dirty aims.” Speaking at the meeting, Valery Vakulchik, at the time the head of the K.G.B., confirmed that the Russians belonged to the Wagner Group.
Then, just 10 days before the Aug. 9 vote, Belarusian investigators accused the Russians of plotting to disrupt the election.
“Russia is afraid of losing us,” said Mr. Lukashenko, accusing the Kremlin of trying to “suffocate” Belarus.
Russia, long accustomed to Mr. Lukashenko’s eccentric ways but shocked by his sudden burst of open hostility, offered its own bizarre explanation of what the men were doing at the sanitarium. The Russian ambassador in Minsk claimed that the men had simply missed a flight at the airport and needed a place to stay before catching another, but there was no explanation as to why they had chosen rooms in a resort on the opposite side of town, away from the airport.
For staff at the sanitarium, the news that their guests were part of a covert Russian military operation to sow chaos only compounded their own confusion.
Yelena, a housekeeper in the building where the men stayed, said she was surprised to find out that the Russians had anything to do with the military.
“They didn’t look like fighters, only a few looked strongly built,” said Yelena, who refused to give her last name for fear of repercussions from the management. “They were behaving well, very culturally, they went to the outdoor gym,” she said. “Perhaps, they underwent some medical treatment, took baths.”
The resort — called Belorusochka, which means “a Belarus woman” — seemed an odd choice, more a time machine for people nostalgic for the Soviet Union than a place anyone interested in plotting a coup would ever stay.
Standing on the shore of a picturesque reservoir, the resort is surrounded by a fence and resembles a prison camp more than a spa. In keeping with the penitentiary motif, every activity is governed by strict rules and the iron will of Svyatoslav F. Savitsky, the chief doctor, who drives around the grounds in his S.U.V., forever on the lookout for suspicious activity.
“I haven’t been to a resort like this since I was 12,” said Olga Matuzo, a 42-year-old Russian who had traveled 1,500 miles from the Russian city of Chelyabinsk with her sick mother. “Immediately after you come to the reception area you feel like you are in the Soviet Union.”
She said she definitely wouldn’t be coming back, complaining that the staff were grumpy and that the bed in her room collapsed after she sat down on it. Even her mother, familiar with Soviet standards of hospitality, was appalled by the conditions, she said.
Also unlikely to return are the arrested Russians, who, the Belarusian authorities now insist, were never up to any mischief in Belarus but were the victims of an elaborate plot engineered by Ukraine’s secret service in cahoots with the United States.
According to this new version of what happened, the men had been lured to Belarus by Ukrainian spies, who planned to seize their plane as it flew over Ukraine and have the men arrested over their role fighting in eastern Ukraine.
That Belarus has changed its story so dramatically is a measure of how swiftly the country’s strongman leader, Mr. Lukashenko, has reassessed his political interests.
Barraged with street protests after he claimed a landslide victory on Aug. 9, Mr. Lukashenko abruptly dropped his accusations against Russia and began pleading with Moscow for help. He called Mr. Putin four times by telephone and sent his oldest son, Viktor, to the prison holding the Russians to make sure they were being well fed.
On Aug. 14, after failing to curb an initial round of street protests with a frenzy of police violence, he ordered the Wagner mercenaries released and allowed them to return to Russia. All charges against them were dropped. The protests have continued to consume the country, with tens of thousands turning out in Minsk and dozens rounded up by the security services on Sunday.
Upon the mercenaries’ return to Russia, several of them appeared on Russian television, claiming that they had no connection to the Wagner Group and had simply stopped off in Belarus en route to Venezuela, where they had a job lined up guarding an undisclosed Russian facility. Shortly after, the K.G.B. chief, who presided over their arrest, was removed and replaced with a new security chief seen as friendlier to Moscow.
The spa would like to forget the whole affair. Anastasia G. Bychko, the head of its marketing department, declined to discuss the mercenaries but bubbled with enthusiasm about all her sanitarium has to offer. “Our main attractiveness is the broad range of medical services that we can offer,” she said, adding that first-time guests are so impressed, “they always come back.”
Ms. Step, the resort’s nightclub D.J., hopes that the experience of the Russian men will not deter others from visiting. Most guests, she said, are women, so the place could do with more male visitors. To try to correct the gender imbalance, she has told guards at the entrance checkpoint that every male guest who enters “should be awarded with a bottle of vodka.”