In the far future, the galaxy is governed by the Mercatoria - a vast bureaucratic authority that controls interstellar travel through its monopoly on wormhole access. When war comes to the remote Ulubis system, scholar Fassin Taak is sent on an urgent mission among the Dwellers - ancient, gas-giant-dwelling beings who have existed for billions of years and may hold the secret to a legendary lost network of wormholes that could reshape the balance of power in the galaxy. Meanwhile, an invasion fleet led by the pirate-king Archimandrite Luseferous bears down on Ulubis, and time is running out. Iain M. Banks' grandest space opera outside the Culture, a novel about deep time, ancient civilisations, and the gap between what we seek and what we find.