So he's lost his memory, but he's sure there's some terribly important thing he knew that he just has to tell people. And as his mind starts coming back, he finds that the black hats are chasing him and want to make sure they can shut his mouth permanently before he...
I know. It's been done so many times that I'm sure you lost count years ago. I certainly have. But here's one detail I really liked. The aforementioned black hats are close behind him, he's in this deserted park, and he runs into this guy. He whips out his blaster, kills him, swaps clothes, then quickly vaporises the remains.
So he escapes, fully recovers his memories, gets the message to the right place and saves the world. And then someone says, remember the guy you killed in the park when you were on the run?
Um, yes, he says uneasily.
Well, they continue, he was on his way to meet his wife. They first met at that exact spot, and every year they met there again on their anniversary. But now he won't be meeting her any more.
Even though the end justifies the means a million times over, he's absolutely stricken by the realisation of what he's done and spends the rest of his life trying to make amends. Austin Powers did this idea too in a comic version, but Asimov was first and I thought his treatment was at least as good.