The film, which is excellent, is based VERY LOOSELY on a true story from 1979 pertaining to the Iranian hostage crisis. How loosely? I Googled "Canadian caper" this morning to find out. "This knocked me out" department: In the narrative of the actual event, the bulk of the movie's second half simply doesn't exist.
In reality, the CIA guy got into Iran, picked up the US diplomats who had been hiding out at the Canadian ambassador's residence, and left the country in a single day, using the (seemingly absurd) cover that they were all part of a Hollywood sci-fi film team that had been looking at locations in Iran. The Iranians bought it. The six Americans and the CIA guy escaped.
Promising -- but boring, right? That's the problem with reality. It's usually dull. You get to the airport. You show your passports. You get on the plane. You leave Iranian airspace. What kind of a suspense movie would THAT be?
The best part of the film was the lie that emerged from the premise supplied by the actual event.
Virtually all of the intense drama of the second half of the film -- the dangerous scouting of the supposed locations for "Argo" scenes, the cat-and-mouse game with the Javert-like Iranian figure who suspects something is up, the abrupt news that the the mission has been called off due to second thoughts in Washington, the protagonist's decision to disobey orders and head to the airport anyway, the final approval of the President once the mission is underway, the cars full of militants pursuing the airport down the runway -- all of that was made up. None of that actually happened. It was all added by the gifted screenwriter, Chris Terrio.
At the end of the day, I think every story worth reading or watching is somehow "based on actual incidents." The question is what interesting lies we will add. I found studying what was added to this gripping story an important lesson in plot development, in raising stakes for the protagonist and pushing him, and his cause, to the outer limit, in not letting the "truth" -- or any boring variation on it -- get in the way of that.