This is the installer for Cthulhu: An Unspeakable Mod for Half-Life v1.0
Cthulhu is a single-player modification for Half-Life.
It contains 65 maps, 21 new monsters and 14 new weapons.
Aeons ago, Earth was ruled by The Great Old Ones, beings so alien and terrible that merely seeing them would drive most people mad. Before man's ancestors climbed down from the trees, these being were defeated in a war with The Elder Gods.
But their alien nature meant that they could not be slain in any way that we would understand, so they were imprisoned.
And so they wait, patient and potent until the stars are right and they shall walk forth once again and wipe mankind from the face of the Earth.
You play Ranulf Stafford, an occult investigator in Arkham in the year 1928. Drawn into a nightmare chain of events, you find yourself the only thing standing between mankind and the return of Cthulhu, one of the most dreadful of The Great Old Ones.