For decades parasites were the pariahs of science. Only recently have biologists begun to appreciate that these diverse and complex organisms are the most highly evolved life forms on earth. In this work, Carl Zimmer takes the reader on a tour of the strange and bizzare world that parasites inhabit, and recounts the voyages of these wonders of creation. Parasites can: rewrite DNA; rewire the brain; genetically engineer viruses as weapons; and turn healthy hosts into the living dead. This book follows researchers in parasitology as they attempt to penetrate the mysteries of these omnipotent creatures who control evolution, ecxosystems, and perhaps the future of the human race.