The opening of Operation Long Jump takes readers inside a meeting between Franklin Roosevelt, Joseph Stalin, and Winston Churchill, held at the British Embassy in Tehran in 1943. The purpose of the summit: how to rid the world of Adolf Hitler. But before the trio of leaders and their senior military advisors can come up with an agreeable plan to win the war, Nazi assassins enter the room, draw submachine guns, and at the orders of Hitler and Heinrich Himmler, murder the leaders of the three most powerful armies in the world.

The assassinations didn’t happen, of course, but after learning when and where the meeting would take place, Hitler set a plan in motion to kill everyone there in one fell swoop. As author Bill Yenne writes in his astonishing work of nonfiction, the decapitation of the Allied Forces was narrowly averted when a Swiss double agent stumbled onto the plot.

During World War II, heads of state were on high alert for assassination attempts. Churchill believed (correctly) that Hitler wanted him dead. Hitler, of course, was in everyone’s crosshairs. (Even the pope wanted to kill him.) Stalin had mortal enemies at home and abroad. With those threats in mind, Tehran was agreed upon as a relatively neutral meeting place. Stalin didn’t want to travel far from the Soviet Union, and, what's more, was scared of flying. Though Churchill and Roosevelt weren’t keen on the location, after long negotiations it became obvious that it was Tehran or nowhere.

And yet, Tehran’s complicated history left it riddled with spies from every corner of the world. American intelligence was still in its infancy in 1943, the Office of Strategic Services having only been established the year before. The British Secret Intelligence Service, however, was robust and complemented by the Special Operations Executive (the “Ministry of Ungentlemanly Warfare,” as rival services called them), whose mission was not only to spy but also to sabotage and assassinate. The Soviet Union, writes Yenne, “maintained an entirely different sort of intelligence apparatus, whose role was intimidation more than intelligence gathering; beating up suspects rather than opening their mail.” Germany’s intelligence network rivaled Russia’s “for brutality and the British services for complexity.”

One local spy in demand was Ernst Merser, a Swiss socialite and businessman who specialized in international trade. Here was a spymaster’s dream: a citizen of a neutral power who spoke several languages and could travel without arousing suspicion. The British recruited him straightaway. The Germans didn’t realize this, and soon attempted to recruit him as well. Merser accepted both offers, and became a double agent working for the British. ...