After crashing into planet 4546B, the player sets out to explore unknown buildings and biomes in the ocean. While exploring planet 4546B, the player discovers an abandoned alien facility, which the player finds an abundant information about the planet. As the player finds crewman logs and alien archives, they discover the Aurora was shot down by an ancient alien quarantine facility to contain a virulent fatal bacteria known as “Kharaa”. Since the player becomes infected by Kharaa, they cannot deactivate the quarantine protocols. Eventually, the player is contacted by a telepathic being, a Sea Emperor Leviathan. The Sea Emperor explains what the Precursor aliens were attempting to do to find a cure for Kharaa. The Sea Emperor Leviathans produce an enzyme, designated “Enzyme 42”, but adults do not produce enough to be effective. The Precursors died before they could discover the required ingredients necessary to allow the hatching of young Sea Emperors.