In the book, Lane discusses what he considers to be a major gap in biology: why life operates the way that it does, and how it began. In his view as a biochemist, the core question is about energy, as all cells handle energy in the same way, relying on a steep electrochemical gradient across the very small thickness of a membrane in a cell – to power all the chemical reactions of life. The electrical energy is transformed into forms that the cell can use by a chain of energy-handling structures including ancient proteins such as cytochromes, ion channels, and the enzyme ATP synthase, all built into the membrane. Once evolved, this chain has been conserved by all living things, showing that it is vital to life. He argues that such an electrochemical gradient could not have arisen in ordinary conditions, such as the open ocean or Darwin's "warm little pond". He argues instead (following Günter Wächtershäuser) that life began in deep-sea hydrothermal vents, as these contain chemicals that effectively store energy that cells could use, as long as the cells provided a membrane to generate the needed gradient by maintaining different concentrations of chemicals on either side.
Once cells similar to bacteria (the first prokaryotes, cells without a nucleus) had emerged, he writes, they stayed like that for two and a half billion years. Then, just once, cells jumped in complexity and size, acquiring a nucleus and other organelles, and complex behavioural features including sex, which he notes have become universal in complex (eukaryotic) life forms including plants, animals, and fungi.
The book is illustrated with 37 figures taken by permission from a wide variety of research sources. They include a timeline, photographs, cladograms, electron flow diagrams and diagrams of the life cycle of cells and their chromosomes.