WASHINGTON — When a former C.I.A. officer was detained overseas recently, Montenegrin officials thought the answer to a question that their country has been obsessed with for two years might be within reach: How did Russia try to topple Montenegro’s government?

On the eve of a parliamentary vote in 2016 viewed as a referendum on membership in the North Atlantic Treaty Organization, the Montenegrin police broke up what they claimed was a Russian-backed coup. The investigation and court proceedings over the ensuing two years have riveted the country, including the sensational, and head-scratching, allegation that the coup backers recruited a former C.I.A. officer to help ferry its plotters out of Montenegro.

The former officer, Joseph Assad, insisted it was all a huge mistake. He denied knowing of any Russian involvement in Montenegro and said he was only advising a friend hired as the opposition’s campaign adviser.

The Montenegrin controversy is a prime example of the sort of mistrust, suspicion and, sometimes, paranoia, that has arisen in the wake of Russia’s campaigns to meddle in European and American elections. Current and former Montenegrin opposition officials argued that government officials’ paranoia has them seeing Russians hiding behind every tree — and prompted them to wrongly tie Mr. Assad to the alleged plot.