What Kira realises by the end of the novel is that the Guardians, the people who are in charge of the society she is a part of and whom she now works for, are far from the benevolent individuals she assumed they were. In her mind, they are represented by Jamison, who is the man who "saved" her at the trial and also encouraged her to use her talents. However, as she sees the chains that entrap the Singer, and also discovers the young girl, Jo, who is likewise kidnapped and kept in captivity, she comes to realise that the Guardians have killed and stolen in order to control the talents of the various children they are keeping:
The guardians with their stern faces had no creative power. But they had strength and cunning, and they had found a way to steal and harness other people's powers for their own needs. They were forcing the childrne to describe the future that they wanted, not the one that could be.
The antagonist in this novel is therefore the group of individuals known as the guardians, whose spokesperson, at least as far as Kira is concerned, is Jamison. What is so intriguing about this novel when you read it for the first time, however, is the way that it remains unclear who the antagonist actually is until Kira begins to work out what precisely is going on around her and begins to piece things together.
The antagonist really was the council members because they tried to keep Kira and the others (Thomas and Jo) captive and make them work. They also lie about there being 'beasts'. (This isn't certain but it is hinted in the book). Antagonist is a person who is the 'bad guy' as people say.
~Hope this helped
(Btw: Im new to this site and all)