When I uploaded the link for Chapter 1, I tested it while logged in to O365. It never occurred to me that the link would behave differently when you weren't logged in.
Guess what, it does.
Screw you O365.
Anyway, the link is fixed now. If you tried to get Chapter 1 previously, and were left scratching your head, you can stop scratching and get the chapter.
(You're also, of course, free to continue scratching, at your discretion).