Reading like a detective story, this work discloses the curious history of the dramatic rise and swift fall of the concept of the "Fifth Force", a proposed modification of Newton's Law of Universal Gravitation and one of the most heralded and publicized physics theories in recent memory. While discussing the origin and fate of this short-lived concept, the author provides an analysis of the ways in which scientific hypotheses in general are promulgated and pursued. This book is aimed at general science readers.