The Locked Tomb is a four-part science-fantasy epic space opera with complex societal and magic systems. Gideon the Ninth introduced the setting and the societal conventions, while Harrow the Ninth delves into the intricacies of Muir’s worldbuilding.

Roughly 10,000 years ago, Earth faced inevitable mass extinction from human-induced climate change. Wealth disparity grew so large that the richest people on Earth were trillionaires. A Kiwi man named John, alongside a ragtag group of allies, tried to save humanity through a science project and became embroiled with necromancy. John used this necromancy to both kill and revive the entire planet in an act called the Resurrection. The Resurrection placed John as the God of humanity and an Emperor at the seat of a newly founded necromantic empire. Humanity was then split up along the nine planets of the solar system (including Pluto) and divided into Nine Houses, according to the whims and specialties of John’s closest and most trusted disciples. John turned those disciples into Lyctors, demigod-like necromancers. Becoming a Lyctor requires consuming the soul of another living human being, often one very close to the necromancer called their cavalier, in order to use that soul as a battery.