Pure HP Lovecraft.....!
An apparently "normal" American family falls into the clutches of a mysterious, indestructible, underderground-dwelling "Elder Race" that may (or may not) have come down from the Stars, its existence and nature discerned only by neolithic Native American Shamans who have attempted to transmit their discoveries down through the ages via pictographic symbols....Snake totems, shape-shifters...Wow!
Typical "Lovecraftian" ending, too...The Cthulu Mythos LIVES!!