Subnautica takes place in the late 22nd century, when humanity begins to colonize planets in space. A vessel constructed by the trans-gov Alterra, known as the “Aurora”, has been sent to the outer reaches of controlled space on its maiden voyage with the goal of constructing a form of high speed space travel structure known as a Phasegate. The Aurora was chosen for this mission due to its new, advanced scanners, and to find a lost ship, called the Degasi, which crashed on planet 4546B long ago. While the Aurora was cruising around the planet, it was hit by an unknown energy pulse, resulting in catastrophic hull failure, which then crash landed on 4546B. Several lifepods are jettisoned from the Aurora as it was crashing, one containing the player. The other lifepods’ inhabitants perish through various means, leaving the player as the only survivor. The player finds records of the Degasi crew but two are confirmed dead and one is presumed dead.
The player also learns of the existence of the “Precursors”, an alien race that came to this planet to research a bacteria called the “Kharaa”. 4546B is under automated quarantine due to the bacteria escaping in an accident. The Quarantine Enforcement Platform shoots down ships that attempt to leave, land or enter orbit in order to stop the bacterium from spreading to other worlds. The player witnesses this happen when another ship, the Sunbeam, detects the Aurora’s distress signal. The Sunbeam tries to land to attempt a rescue but is shot down. When the player attempts to deactivate the installation it fails due to the player being “infected”. In order to leave the planet, the player must find the Precursors’ base deep underground to find the Sea Emperor Leviathan. It has been keeping the life in the area alive by using small creatures known as “Peepers” to distribute small amounts of a degraded form of the cure. This keeps the flora and fauna from dying but it is insufficient and not of high enough quality to eradicate it from the ecosystem. It asks the player to help it hatch its eggs because the young produce the cure, known as “Enzyme 42”, in a purer form. Once the player hatches the eggs, they are cured of the infection and are free to leave the planet, ending the game.