Titus Crow and his companion Henri-Laurent de Marigny confront an ancient, subterranean threat that seeks to dismantle human civilization and the fabric of reality itself. Driven by the discovery of cosmic horrors lurking beneath the Earth's crust, Crow utilizes advanced technology and arcane knowledge to navigate the perils of space-time. As the Great Old Ones exert their influence over the waking world, the protagonists must traverse dreamscapes and alien dimensions to prevent the total collapse of the universe. The narrative unfolds through a series of high-stakes encounters, emphasizing the vulnerability of humanity against entities of immense, incomprehensible power.

This omnibus serves as a definitive collection for readers interested in the expansion of the Cthulhu Mythos beyond the original Lovecraftian canon. The work is characterized by its shift toward a more action-oriented, pulp-inspired approach to cosmic horror, contrasting with the slower, atmospheric dread typical of the genre's origins. Lumley's prose emphasizes the scale of the threat, focusing on the mechanics of the battle against the Great Old Ones rather than purely psychological disintegration. The collection is likely to appeal to those who enjoy high-concept science fiction blended with dark, supernatural elements.