Slaves of the Mastery by William Nicholson

When the ruthless soldiers of the Mastery strike, the city is burned, and the Manth people are taken into slavery. Kestrel Hath is left behind, separated from her beloved brother Bowman, and vowing revenge. Now Kestrel must find Bowman again, and Bowman must learn the secrets of the Singer people. Only then will they break the power of the Mastery. Slaves of the Mastery by William Nicholson