In addition to the fact that we have to find this artifact that launches the portal, which will later send the hero to the past, but also launch him. Sam is sent to the territory of the Pyramids, where the "Key of Eternity" is located. Humanity actively opposed him in space, but the alien creature did not stop the pressure and decided to seize the entire Earth. The actions of Cool Sam 3 begin 3 years after the start of the war with Mental (Tah-Uma). Sam will fight not only with God, but also with his armies.
These actions attracted the attention of Tah-Um and his countless armies, which he cloned every minute. Intergalactic flights became available, space travel became entertainment. When humans found the remnants of civilization from Sirius, their progress surpassed all expectations. In a first-person shooter with an FPS style, Serious Sam will fight against Tah-Uma - the oldest god of the cosmos and the god of a small galactic space. The materials found replaced almost all of the earth's resources. Due to the found fossils, in Serious Sam 3: BFE scientists begin to accelerate material processing, study engineering and advance science. In the middle of the twenty-first century, mankind found on the territory of Ancient Egypt the remains of another civilization that arrived from the planet Sirius. Tough Sam's story begins long before he was sent back in time.