The Fiery Heart (Bloodlines, #4)

Sydney Sage is an Alchemist, one of a group of humans who dabble in magic and serve to bridge the worlds of humans and vampires. They protect vampire secrets and human lives.
In The Indigo Spell, Sydney was torn between the Alchemist way of life and what her heart and gut were telling her to do. And in one breathtaking moment that Richelle Mead fans will never forget, she made a decision that shocked even her. . .
But the struggle isn't over for Sydney. As she navigates the aftermath of her life-changing decision, she still finds herself pulled in too many directions at once. Her sister Zoe has arrived, and while Sydney longs to grow closer to her, there's still so much she must keep secret. Working with Marcus has changed the way she views the Alchemists, and Sydney must tread a careful path as she harnesses her profound magical ability to undermine the way of life she was raised to defend. Consumed by passion and vengeance, Sydney struggles to keep her secret life under wraps as the threat of exposure and re-education looms larger than ever.
Pulses will race throughout this thrilling fourth installment in the New York Times bestselling Bloodlines series, where no secret is safe.