KIRKENES, Norway — Frode Berg says he never meant to be a spy.

Mr. Berg, a silver-haired Norwegian pensioner known by his neighbors to have a soft spot for neighboring Russia, was 60 when an acquaintance in his Arctic hometown recruited him in 2015 to work for Norway’s military intelligence. Over the next two years, on five trips across the border, Mr. Berg acted as a courier — mailing relatively small sums of cash and encrypted memory cards to a woman in Moscow he knew nothing about.

Then, one December morning in 2017 when he was in Moscow, Russian agents swept him up, bundled him into a brown Volkswagen van and sped him to the old K.G.B. headquarters. He spent the next two years in prison where, by his own account, he was treated fairly well.

Now, finally free, Mr. Berg is angry — but not at Russia.

“I was under pressure from the military intelligence service in Norway,” Mr. Berg, a former inspector along the Norwegian border with Russia, said in an interview after his release in a prisoner swap in November. “I trusted them that they will not send me to something dangerous in Russia. And they did.”

Mr. Berg was, by all appearances, a small-time player in a botched intelligence operation. But his tale embodies the tensions emerging as Western countries intensify their hunt for the Kremlin’s secrets.