So Jon likely joined the Magnus Institute to find out what exactly happened with Mr. Spider. But we don’t really…ever find out? I mean, all we know is why Leitner’s name is on there (and who he is) and that it’s affiliated with the Web. But that doesn’t really tell us anything. I mean, Jon already knew it was a cursed spidery book. We don’t really get that much further into the details. (Not that we do with most of the monsters or artifacts.)