From the back of the book:
The Empire stands victorious over its enemies at last. With her chief rival cast into the abyss, Empress Seda now faces the truth of what she has cost the world in order to win the war. The Seal has been shattered, and the Worm stirs towards the light for the first time in a thousand years. Already it is striking at the surface, voraciously consuming everything its questing tendrils touch. Faced with this threat, Seda knows that only the most extreme of solutions can lock the Worm back in the dark once again. But if she will go to such appalling lengths to save the world from the Worm, then who will save the world from her? The last book in the epic critically acclaimed Shadows of the Apt series.
The Shadows of the Apt series as a whole has been one of the most inventive and utterly unique series I've had the pleasure of reading - and - despite SEAL OF THE WORM being book 10 (and the final) there was well enough content and stories to warrant further installments. This is both a sign of quality writing, engaging plotting, and conceptually brilliant world building.
Unlike my reviews for other books in the series I won't focus on the plot as I'm likely to give something away but I will say that SEAL OF THE WORM concludes The Shadows of the Apt in the best way possible. All the plot threads converge and seamlessly intertwine culminating in a tense and action packed conclusion.
There is capacity for author Adrian Tchaikovsky to explore events such as the Twelve Year war and numerous threads post SEAL OF THE WORM which could lead to a new chapter in the epic saga that is Shadows of the Apt - here's hoping.
In a word: Exceptional, I can't recommend SEAL OF THE WORM and the 9 books preceding enough - they are simply a must read for fans of fantasy fiction.