From the publisher:
The Dreaming Prince is a supplement to Chaosium’s Call of Cthulhu Roleplaying system. This particular supplement is driven to explore the extra-human consciousness of the Great Old Ones, in particular Cthulhu. Cthulhu, in his namesake story, remains dreaming in sunken R’lyeh, transmitting his madness to the world around him at different times and to different people based off their sensitivity to such phenomena.
In a bit of a twist off the original story -- albeit not a large one -- the Great Old Ones represented here can be both tangible entities and intangible representations of natural forces beyond what human science can understand. Few of the Great Old Ones are represented here, largely for the sake of time and convenience, and in the course of these adventures, the investigators will never directly encounter the Great Old Ones. Nonetheless, this setting does employ the Mythos both in species and technology. In fact, several human technologies, displayed here as experimental and purely science fiction, are indirectly influenced by the Great Old Ones through a form of mental osmosis.
This work contains a scenario from the 1920s that pertain to another two scenarios later in the work in modern times. This understandably involves two separate groups of investigators played by the same players. There are a few recurring motifs throughout the work, as well as unmentioned plot devices that can either gain or lose significance based on how much of the mystery is unraveled.