Aelin Galathynius, once known as the king's assassin, is the heir to a nation that was taken over by the king of Adarlan. With her allies and friends, she plans on freeing the continent of the tyrant king’s chokehold and retaking her throne.
The king of Adarlan is a tyrant who has been steadily taking over the continent and wiping out magic. He wants to take over the world, and he is ready to use his army of soldiers possessed by mythical demons to do it.
Aelin reveals her first stage of publicly defying the king by breaking her cousin Aedion out of the castle. After causing a distraction, she escapes with Aedion, undermining the point of Aedion's capture and turning what would have been his execution into a show of her power.
Aelin meets with Arobynn Hamel, the "King of Assassins" and her former mentor. She strikes a deal with him in exchange for his support in part of her plans against the king. Their bad history impedes negotiations, but Aelin manages to overcome her past and trick him to gain the upper hand.
Aelin reassumes her alias as the king's assassin and pretends to capture her friend Chaol, a rebel who used to work in the palace, to get an audience with the king. The confrontation is tense, since she doesn't know if he knows her true identity as the heir to Terrasen.
I predict that the king will reveal that he is aware of Aelin's true identity, leading to a final showdown between them. Aelin's friends will launch an assault on the castle while she and the king have a one-on-one battle. The ending might show the rebels claiming victory and bringing magic back to Adarlan.