Somewhere near Moscow.
Sept. 26, 1983.
Stanislav Petrov, a lieutenant-colonel in the military intelligence section of the Soviet Union's secret service, reluctantly eased himself into the commander's seat in the underground early warning bunker south of Moscow.
It should have been his night off but another officer had gone sick and he had been summoned at the last minute.
Before him were screens showing photographs of underground missile silos in the Midwest prairies of America, relayed from spy satellites in the sky.
He and his men watched and listened on headphones for any sign of movement - anything unusual that might suggest the U.S. was launching a nuclear attack.
This was the height of the Cold War between the USSR and the U.S. Both sides packed a formidable punch - hundreds of rockets and thousands of nuclear warheads capable of reducing the other to rubble.
It was a game of nerves, of bluff and counterbluff. Who would fire first? Would the other have the chance to retaliate?
The flying time of an inter-continental ballistic missile, from the U.S. to the USSR, and vice-versa, was around 12 minutes. If the Cold War were ever to go 'hot', seconds could make the difference between life and death.
Everything would hinge on snap decisions. For now, though, as far as Petrov was concerned, more hinged on just getting through another boring night in which nothing ever happened.
Except then, suddenly, it did. A warning light flashed up, screaming red letters on a white background - 'LAUNCH. LAUNCH'. Deafening sirens wailed. The computer was telling him that the U.S. had just gone to war.
The blood drained from his face. He broke out in a cold sweat. But he kept his nerve. The computer had detected missiles being fired but the hazy screens were showing nothing untoward at all, no tell-tale flash of an missile roaring out of its silo into the sky. Could this be a computer glitch rather than Armageddon?
Instead of calling an alert that within minutes would have had Soviet missiles launched in a retaliatory strike, Petrov decided to wait.
The warning light flashed again - a second missile was, apparently, in the air. And then a third. Now the computer had stepped up the warning: 'Missile attack imminent!'
But this did not make sense. The computer had supposedly detected three, no, now it was four, and then five rockets, but the numbers were still peculiarly small. It was a basic tenet of Cold War strategy that, if one side ever did make a preemptive strike, it would do so with a mass launch, an overwhelming force, not this dribble.
Petrov stuck to his common-sense reasoning. This had to be a mistake.