In this book, molecular biologist Alina Chan and science writer and zoologist Matt Ridley present the alternative theories for the still unknown origin of the Covid-19 virus. Is the pandemic the result of natural spillover of virus from bats, possibly through an intermediate animal host, or is it the result of a leak from a virology laboratory in Wuhan, probably Wuhan Institute of Virology (WIV)? The main argument for natural spillover is that this has occurred repeatedly in the past, resulting in a number of epidemics, e.g. with HIV, Ebola and the SARS virus. However, no evidence has been found for this theory. No intermediary hosts have been found in spite of examination of thousands of animals. Concerning a laboratory leak, the authors emphasize that they consider theories postulating deliberate laboratory construction of the virus as a biological weapon as unlikely. On the other hand, they consider a laboratory leakage associated with coronavirus research plausible, either with waste material from the laboratory or through an infected laboratory worker. Recognizing that no definitive evidence has been found for this theory, they nevertheless present a series of facts which together make laboratory leakage a viable alternative to natural spillover. The authors describe several serious obstacles to the efforts to clarify the origin of the pandemic. Firstly, the Chinese authorities have consistently obstructed this work. Secondly, certain Western scientists with links to WIV and China have tried to suppress the laboratory leakage theory, until recently with success. The authors' presentation of the alternative theories is balanced, even if one suspects that they favour the leakage theory.