The weird and wonderful ways in which parasites make a living.
This is a fascinating trip into the world of the parasite. The book's subtitle describes this world as bizarre, but the adjective hardly does it justice. If there's an ecological niche inside a potential host's body, there will be a parasite to fill it, it would seem. There are parasites that live only in the Achilles' tendons of deer; there are parasites whose life-cycles carry them from snail to ant to cow's liver; there are parasites that turn crabs into spayed zombies who nurture the parasites' own offspring.
If Nature really does have an intelligent designer*, then it's a designer with a twisted sicko's imagination.
The second half of the book descibes the evolutionary arms races that take place between parasite and host, and makes an interesting case for parasites' being a major factor in the evolution of life on earth.
* It doesn't, by the way.