The educated public have long been regaled with “the mysteries of quantum physics”, which enshroud far-flung claims about the fundamental nature of matter. These rely on a stunning proposition of quantum theory arising in the 1960s and contested through the subsequent sixty years: that the probabilities deriving from it defy a mathematical inequality known as Bell’s inequality. John Bell himself, who formulated the problem, was puzzled by the result, and surmised that in time we would discover what is wrong with its characterisation of the matter. In this book, Frank Lad claims to have identified the mathematical error that gives rise to the misunderstanding. Addressed as a challenge to the physics community, its content is accessible to any generally educated reader who is familiar with university-level concepts of linear algebra and functions of several variables. Understanding of complete mathematical detail is not required for appreciation. Largely ignored and dismissed by the scientific community of professional physicists, here is the background to the result, and the resolution to the controversy.