It's easy to make fun of flat earthers but this book shows that they sit at the intersection of a lot of other conspiracy theories, and share a lot in common with cults. Weill goes through the history of the movement, in the 19th Century (it's not old, the Greeks had already figured out that the Earth was a globe). But, surprise surprise, it is really with Youtube and Facebook that the contemporary movement took off (see what I did there?) thanks to their recommending algorithm. And yes, flat earthers gravitate in the same orbit (natch!) as antisemites (if there's a conspiracy, there have to be conspirators), neo-Nazis, Q, and vaccine troofers. So it's not a movement of harmless eccentrics who can just be ignored. They join the crowds of radicalized by social media. It's not cute. It's dangerous.