Sometimes the people you trust the most are really the people you should trust the least.The most innocent looking people can be the villain of the story.
In this world there are two of types of species: There are humans who posses no powers and supernaturals who have some powers.
Supernaturals were once human. They technically still are, but there DNA was messed with causing them to have powers. Supernaturals are hated by humans. Humans find it unfair that they have these amazing powers and they don't. So...humans hunted the supernaturals. Dropping the supernatural population to 1%. And that 1% is still being hunted.
Some of the supernaturals decided to side with the humans so they could live. They would be use as weapons for war but still treated like human. That was the deal.