In Gun Metal Heart by Dana Haynes, Daria Gibron, a freelance operative with a long and deadly history, has been slowly recovering from the injuries sustained from her last case. Hiding out in a town in rural Italy, she has been staying as far off the map as she can—until she's tracked down by an old colleague. Diego had been a bodyguard in Florence, protecting an engineer and her invention, when they were attacked by a highly trained paramilitary group. Diego alone escaped and the White Scorpions, a Serbian mercenary group known for their indiscriminate violence, are now after him. Well, after him and Daria, now that he's dragged her into the picture.

At the same time, a small group of disgraced CIA agents have been waiting for their chance to exact revenge on the person they blame for their discharge—Daria Gibron. When they learn she's in contact with Diego, they get the okay from their former bosses to take her out. With several highly trained teams out to get her, a partner withholding critical information, and a missing invention around which everything turns, Daria is in the worst danger of her life. And she couldn't be having more fun.