Reign of Demons is the third and final installment in the War of the Last Days series, written by Karim Soliman. Ogonians seem unstoppable, a force that has decimated each Goranian city; the fortress of Karun is the last obstacle between them and their promised land. The same stronghold Nadine is trying to control, in an unstable ally with the Skandivians; tension between sides is rising.

At the same time, after what they were told by Nelly, Zahra and Halgrim are trying to continue their voyage to the Frozen Cave, with an itinerary that will bring them to the city of Inabol; and which later will take them to discover more about the secrets hidden under the Goranian Land. The Frozen Marble can be the answer to the Goranian problem, but the cost of using it is too high.
Leila is in a complicated position. After being kidnapped into the Koyan side, she's offered a deal: saving a few Goranians if she collaborates with the destruction of the rest; when a defeat seems probable, taking a stance on it becomes quite difficult. And it becomes even worse when she's sent to Karun in order to end with the resistance to the Ogonian army.

All of those threads, plus some additional ones (Frankil with the Wandering Seer), get woven in this last installment, and all of them bring us to a decisive moment that will shape Gorania as we know: the battle of Karun. But despite being this one of the most decisive moments in the saga, Soliman also takes this book as a way to continue expanding Goranian history and lore, foreshadowing things that I hope get explored more in a future new series. 
And what I can say about the battle of Karun, and all that surrounds it without being too spoily; an epic battle told from the POV of several characters that acts as the perfect close point to the series, about 120 pages where you just want to continue reading and see how all it ends, low-key hoping your characters survive. It will keep you on the edge of your seat for all of it.

While I think this is a really strong book, I found the pacing to be a little irregular around the middle section, as the expansion Soliman brings to Gorania can drag the plot a little; outside of that detail, it's an authentic pageturner.

Reign of Demons is the golden tip that puts an end to the War of the Last Days saga; if you like epic fantasy, you should try this series. I can only congratulate Karim Soliman for the amazing payoff this book has been for the rest of the series.