A forgotten hero of the psychedelic 1960s must confront a reality-bending former ally to prevent a global catastrophe. Once known as the Man of Muscle Mystery, Flex Mentallo is drawn back into action to investigate the nefarious schemes of The Fact, a former comrade whose reality-warping powers threaten to unravel existence. A mysterious rock star, whose connection to Flex is deeply personal, may hold the key to understanding and combating this existential threat. The narrative unfolds through a lens of surrealism and meta-commentary, questioning the nature of heroism and reality itself.

Flex Mentallo is widely recognized as a seminal work of psychedelic superhero fiction, celebrated for its ambitious narrative and deconstructive approach to the genre. Critics often highlight Grant Morrison's distinctive writing style, which blends complex philosophical ideas with vibrant, often bizarre, imagery. Readers frequently praise its unique take on heroism and reality, though some find its dense, meta-fictional layers challenging. The series is noted for its exploration of the power of belief and its impact on the perceived world, solidifying its status as a cult classic within the comic book community.