Blood Ties. Book 4. Fiery Heart

Sydney Sage has to hide too much from her beloved younger sister Zoe, who now works alongside her. Communication with witches. Personal life. Magical experiments. Zoe is wholeheartedly dedicated to the mission of the alchemists and their authoritative father. If... she learns any of her sister's secrets, she will surely turn away from her. Does Sydney have a chance to show Zoe that life is not limited to blind service?
Meanwhile, Adrian is performing real wonders with spirit magic — perhaps this will one day help him gain protection from strigoi. But the cost of what has been achieved is becoming more terrifying, so he will have to decide whether his amazing abilities are worth the madness that follows? 

This is a reissue of the fourth book in the "Blood Ties" series, which expands the popular universe of "Vampire Academy."