Astrobiologist Lewis Dartnell asks what knowledge would be needed to rebuild technological civilization after a catastrophic collapse - and then proceeds to explain the essential sciences and techniques. The book covers agriculture, food preservation, materials science, metallurgy, medicine, communication, transportation, and energy, showing how each depends on the others and how all trace back to fundamental principles of physics and chemistry. Dartnell writes as if addressing actual survivors, explaining not just what they would need to know but in what order to learn it. The book reveals how much of what we take for granted depends on global supply chains and accumulated expertise that would not survive societal breakdown. Yet Dartnell is also hopeful, showing how the scientific method itself could be reconstructed and how understanding basic principles would enable rebuilding. The book works both as speculative survival guide and as a tour of the knowledge that underlies modern life - readers finish understanding their own world better. Dartnell, whose academic research concerns the possibility of life on other planets, brings scientific rigor and accessible prose to this thought experiment. For anyone interested in how technology works, how science developed historically, or how resilient our civilization actually is, this book provides both education and provocation.