From the back cover of the 5th edition rulebook:
| DEAD CTHULHU WAITS DREAMING
The Great Old Ones ruled the earth eons before the age of humankind. Remains of their cyclopean cities can still be found on remote islands in the Pacific, buried amid the shifting sands of vast deserts, and in the frigid recesses of the polar extremes. Originally they came to the world from out of the sky. Now they sleep — some deep within the enveloping earth and others beneath the eternal sea, in the drowned city of R'lyeh, preserved from the waters by the spells of mighty Cthulhu. When the stars are right they will rise, and once again walk the earth.
Call of Cthulhu is a roleplaying game based on the works of H.P. Lovecraft, in which ordinary people are confronted by the terrifying beings and forces of the Cthulhu Mythos. Players portray investigators of things unknown and unspeakable. Except for dice, everything needed for play is included in this book.