Sam's letter

Next day, Charley drew three hundred dollars from the bank and exchanged it for about two hundred dollars of old-style currency. He meant to go back to the third level and buy the tickets to Galesburg. But he could never find that corridor again.

Louisa was worried when he told her, and did not want him to look for it any more. But after a while she grew interested, and every weekend they searched together.

Then his friend Sam Weiner disappeared. Nobody knew where he had gone, though Charley half suspected: Sam was a city boy, and Charley had often told him about Galesburg.

One day Charley was looking through his collection of stamps; he had started it with his grandfather's. There he found a first-day cover, an envelope posted on the first day a stamp is issued, that he was sure had not been there before. It had been mailed to his grandfather at his home in Galesburg, and the postmark said July 18, 1894.

Inside was a letter, from Sam. He wrote that he had found the third level, and was living happily in Galesburg in 1894. He asked Charley and Louisa to keep looking for it, because life there was everything they had imagined. He had set himself up in the hay, feed and grain business, since he could not be a psychiatrist in 1894.

That is the story's twist. Sam was Charley's psychiatrist, the very man who told him the third level was only a dream, and he was the one who escaped into the past first.