The series stars Sydney Chandler, Alex Lawther, Essie Davis, Samuel Blenkin, Babou Ceesay, Adarsh Gourav, and Timothy Olyphant in main roles. It is set two years before the events of the 1979 film Alien in an alternate timeline set outside the main canon of the Alien universe. The opening of the first episode introduces the series' central premise: humanity's pursuit of immortality through three paths—cyborgs, humans enhanced with biomechatronic body parts; synthetics, fully artificial beings endowed with intelligence; and hybrids, synthetic bodies containing transferred human consciousness.