The book attempts a historical, epistemological, and broadly philosophical analysis of the evolution of physical theories, their foundations, and their philosophical implications. As an introduction, a brief overview of the perceptions of ancient Greek philosophy is presented, primarily of Presocratics.

The book aims to explore the foundations of quantum mechanics; however, it inevitably addresses issues arising from Einstein's theories. Its title also signifies the fact that Einstein, one of the towering giants of modern physics, introduced a "demon" into microphysics: the hypothesis of hidden variables, meaning the idea that by introducing supplementary, "hidden" parameters, it would be possible to achieve a causal foundation and formulation of quantum mechanics.

In this third revised edition, two chapters have been removed and three new ones added to fully meet the subtitle of the book: Causality and locality in Physics. Several linguistic improvements, some but significant additions, and references to more recent literature have also been made.