The complete back issues of this magazine—all 1,680 of them—are stored in a walk-in closet in our New York offices. We don’t often visit the place. It’s musty and locked, and only one person keeps a key. But to put together our May issue on the Future of Flight, which arrives the same month that Edward L. Youmans founded Popular Science Monthly in 1872, we spent many hours there. During our sojourn, things took a turn for the strange.

We were tracing the history of aviation through the pages of PopSci when we found, in our December 1928 issue, a note. It appeared to be a list of other issues—all flight-related. It had a Web address, too. And it was written on modern PopSci stationery. We visited the URL and discovered an encrypted page within our online archives. We asked our IT department to access it. They couldn’t. But while they were trying to hack in, they discovered that others had visited, and recently; there had been a spike in traffic.

Was whomever was going there the same person—or people—who broke into our closet? What does the note mean? Who wrote it? And to what purpose? Could it help us get into the encrypted archive?

Please help us piece this together. We’ve scanned and posted the note (above) and the covers of the issues it seems to list. Can you make any sense of it? Sure, it might just be some practical joke. But something tells us it isn’t.