The story follows occultist Titus Crow and his friend Henri-Laurent de Marigny as they uncover a plot by the Chthonians and their masters against the people of Great Britain. The two eventually join up with the Wilmarth Foundation, a group of humans with knowledge of the Cthulhu Cycle Deities, and participate in an operation to clear the island of their influence, killing the Chthonian leader in the process. The book ends with the Great Old One known as Ithaqua attacking Crow with his elemental minions, leaving Crow believed dead.
- Titus Crow, a man with extensive knowledge of the Cthulhu Mythos Deities, and an urge to protect mankind.
- Henri-Laurent de Marigny, Crow's friend and fellow occultist, though less experienced. He is the owner of a machine capable of travelling through time and space, dubbed De Marigny's Clock.
- Professor Wingate Peaslee, a senior member of the Wilmarth Foundation.
- Gordon Finch, a telepath in the employ of the Foundation.
- The Chthonians, a race of subterranean beings.
- Cgfthgnm'o'th, the leader of the Chthonians.
- Ithaqua, a Great Old One.
Behind the Mythos
The Burrowers Beneath was first published in 1975.