The reader of this book learns about plate tectonics, bio-diversity, the Wallace Line, and history of the Dutch East Indies Company before reaching the big explosion. Then there's the false start, followed later by the big blast, and then all sorts of stories follow. Then there's more science lessons about tsunamis, shock waves, jet stream, and other stuff. The author strings all these topics together into a most fascinating tale.
I thought the author pushed things a bit too far when he suggested that Krakatoa played a part in the rise of militant Islam in Colonial Indonesia. Anti-colonial feelings were widespread throughout the world, even in countries with no volcano. I found the book's description of the reemergence of the island of Krakatoa in the 20th Century less interesting. His account of visiting the island in person was particularly uninteresting. Perhaps the author was trying too hard to meet a goal of a certain number of pages.
Here's what I find scary. It's going to happen again. That particular spot may not blow in our lifetime, but a similar type of explosion somewhere in that part of the world could very well happen. And Krakatoa isn't the biggest volcano that we know of. Tambora in 1815 was the largest explosion to occur in the past 1000 years and was about twice as big as Krakatoa in 1883. The difference with Krakatoa was that it occurred in the modern era so that news of it spread quickly via telegraph communications. There were also many witnesses in the vicinity and throughout the world who recorded their observations.
As late as 1963 another book was written about Krakatoa that described what happened, but couldn't offer much of explanation as to why volcanoes occur. As it turns out, 1964 was the first year that the theory of plate tectonics first began to be widely accepted by the scientific community. I can remember when I was in grade school (during the 1950s) I commented on the fact that the east coast of South America appeared to mirror the shape of the west coast of Africa. The obvious conclusion was that they used to touch each other. I was assured at the time that scientists said that continents don't move. For once I was smarter than the experts.