Why did symbiotic relationships between prokaryotes become a permanent enslavement, resulting in the eukaryotic cell? This provocative question is at the heart of the book Secret Chambers. “This distinction – between the grubby world of bacteria and the elite world of eukaryotes – can seem deeply puzzling. How is it that some cells remain simple, while others have become so complex during the course of evolution?” (p. 41).To answer this question, Brasier traces both the history of the Earth and the scientists who have studied her. He begins with a chapter where Robert Hooke is given credit for laying out “a kind of Microtopian vision, in which it is microbes that really rule the world” (p. 13), and continues through a dinner party with Charles Darwin, Charles Lyell, and Robert Brown to wind up with his own travels on the Sargasso Sea. Once he sets sail with the foundations of evolutionary thought, he cruises on to discussing ecosystem dynamics through the lenses of fossils and fossil hunters.Coral reefs are the first port of call on the book’s voyage. The fossil history of reef building and collapse is used as a porthole through which the construction of the eukaryotic cell can be viewed. Protozoans, especially Foraminifera, convey the clues to this mystery. “Indeed no living or fossil shell shows this story – from tiny blob, through coiled tube, towards complex colosseum – more clearly through the course of its growth than does one of my favourite little creatures, Discospirina” (p. 102).The final destination requires an exploration of symbioses within Deep Time, leading to the conclusion that modern ecosystems may not provide the best reference point for eukaryotic cell evolution. “If this is a correct reading of the fossil record, it implies that no new kinds of organelle, and no wholly new kinds of algae, have been permitted to arise by symbiosis during the last 540 million years or so. Only in the preceding Boring Billion does the forging of wholly new organelles by symbiosis seem to have been possible” (p. 207).Secret Chambers is as much an autobiographical journey through a career spent in pursuit of these questions as it is an attempt to put forth answers. The level of detail documenting the history behind the science is much more satisfying than the explanation of causal factors resulting in the evolution of complex multicellular organisms. For me to grasp Brasier’s proposal that the “Boring Billion” is at the heart of this transition requires more detail on the science of complexity and system collapse than he presents. However, I do like his analogies, especially the mangrove tree of life and his description of the relationship between a cell and its organelles as rooms aboard a ship.The most useful part of this book for my high school biology class is his categorization of oceanic ecosystems into color-coded types. He ties the colors of the water (blue, green, and brown) with the cycling of nutrients in that ecosystem and the population growth of specific algal types.