It is Sunday 2 October 1983, and Neil Kinnock is striding along the Brighton seafront towards certain victory in that afternoon's Labour leadership election. Few could blame him for feeling cocky. "If you want a real scoop," he says to the press pack at his heels, pointing down at the beach, "I'll walk out there, on the water."
Moments later, posing on the beach, he is caught by an onrushing wave, stumbles, and topples over in an undignified heap. It becomes the abiding image of the conference, even of Kinnock's leadership - a man utterly out of his depth, shamelessly courting the media and making a complete fool of himself in the process.
But what if Kinnock had kept his balance? What if, instead of collapsing on to the shingle as though hit by a sniper, he had stepped aside at the last moment and then posed for pictures gazing out to sea, the man of destiny, the prime minister-in-waiting?
Surely he would have gone into that afternoon's conference a different man - a drier man, certainly. No doubt he would not have allowed Roy Hattersley to lift his arm in that slightly damp gesture of celebration. And in slapping down his new deputy, he would have marked himself out as a strong man, a man not to be trifled with, the kind of man who keeps his footing, even when the tide is against him.
And after that? Kinnock leaves Brighton transformed, his reputation sky-high, his pale grey suit untouched by seawater. When he confronts Margaret Thatcher across the despatch box, he is on masterful form: witty, lucid and, above all, concise. Reporters marvel at his skilful ambiguity during the miners' strike, cheer his cunning ploy of waiting until the moment is right to confront Militant, and swoon in awe as he rips Thatcher limb from limb over Westland. When he travels to the White House to meet President Reagan, the two men are closeted for hours, the American leader desperate for PR tips from the man the Sun is calling the "Great Communicator".
And we all know how the story ends. That famous night in 1987: the "New" Labour landslide, Kinnock punching the air and shouting "We're all right!" at his Sheffield victory rally. He saw off two more Tory leaders, and now his bust stands in the Commons lobby. Thank God he didn't fall over.