The Citadel, a bastion on the protected planet of Dianis, is the third novel in the Dianis, A World In Turmoil chronicles. Achelous, the architect and orchestrator of the planet's defense against extrasolars, has been abducted by the Paleowrights, a powerful religious order. Chained, tortured, and carried off to the Empire of Nak Drakas, Achelous’s fate is unknown.

After the mayhem and outrage of Achelous's kidnapping, Marisa, his mistress and a trader princess, embarks on a mission of restitution. To rescue Achelous, she must go to the heart of her enemy, the Drakan Empire, and save him from Viscount Helprig. The Paleowright clergyman does not care what Achelous may know, just that he has blasphemed the Diunesis faith and shall be hung before the archbishop.

However, the commandant of the Drakan secret service is not so quick to execute. He suspects Achelous is an Avarian, an agent of a galactic federation, the very people the Paleowrights worship as gods.

Amidst the fight against corsairs raiding the planet, attacks by Paleowright armies, and the intervention of the Avaria Federation, Marisa must rescue Achelous, and if successful, can trigger a global war. Can one man be worth that outcome? The answer lies in what he knows.