Mare is on the run. She has a "silver" ability to manipulate electricity, but she has red blood. She teams up with similar people. They are trying to find others and help them to harness their powers. They are on the run and infiltrating Maven's kingdom.
"Silvers" have silver blood. "Reds" have red blood. The Silvers rule and have power over the reds. The reds often work as servants to the silvers. The reds don't like this, so they start some terrorist actions. There is also a war going on between a couple of different Silver/Red factions.
The protagonist lives in this world. She works the streets, pick-pocketing bits from the wealthy. She tries to avoid serving in the war. She lucks out and pickpockets somebody who gives her a job with royals. She discovers that she has lightning powers. The royal family decides to "make" her appear to be a silver. Meanwhile, her brother was killed for his role in the rebellion.
It seems to be a fairly strong metaphor for slavery, with many of the silver not seeing how the reds could not have it any other way.
Eventually, things take a bunch of turns, people that we thought were dead are alive, and revolutions and counter-revolutions break out. It somewhat comes to a conclusion, but is obviously the first book in a series.
