Meagan Spooner 
Skylark [EPUB ebook] 

Vis in magia, in vita vi. In magic there is power, and in power, life. For fifteen years, Lark Ainsley waited for the day when her Resource would be harvested and she would finally be an adult. After the harvest she expected a small role in the regular, orderly operation of the City within the Wall. She expected to do her part to maintain the refuge for the last survivors of the Wars. She expected to be a tiny cog in the larger clockwork of the city. Lark did not expect to become the City’s power supply. For fifteen years, Lark Ainsley believed in a lie. Now she must escape the only world she’s ever known…or face a fate more unimaginable than death.