Slaves of the Mastery is the second novel in the Wind On Fire fantasy trilogy by William Nicholson. It was first published in 2001. The novel's events take place five years on from the closing chapter of The Wind Singer.
A sequel, Firesong, was published in 2002.
Five years have past since the City of Aramanth, of the Manth people, under went its reformation, the walls have been torn down, the poorer houses abandoned, and the entire city has been gripped by a painting craze.
The city, is now a sitting duck for high reaching Marius Semeon Ortiz, and his thousand strong army, encamped near the city. In the city Bowman Hath is uneasy, ever since the power of Morah, an evil influence, and enemy of the singer people, the original Manth, filled his spirit Bowman has been changed, all he knows is that he must carry any burden alone, not with his twin sister Kestrel.
At dawn the following day Marius strikes, taking nearly the entire populace as slaves, the only free survivor is Kestrel, who vows to find her family and repay Marius the injustice he has served her. Meanwhile, the rest of the Hath family, Bowman, His younger sister Pinto and their parents Hanno, and Ira, descended from the ancient Manth Prophet. Travel as slaves to the mastery, a town built entirely on slave labour, the only freeman is the Master, the ruler of the city, who is due to declare on of the habitants of the Mastery as an heir, who will then marry Sirharasi (Sisi), Johdila of Gang, daughter of the ruler of the land, in effect if the marriage went though the master would end up ruling.
Kestrel is found unconscious by the wedding party of Sisi, which includes Sisi's parents and a guard of three thousand armed men, The reason for this being that the commander, Zohon, wishs to marry Sisi himself, Kestrel plays him into thinking that Sisi loves him and to marry her he will need to overthrow the mastery. Sisi and Kestrel, now firm friends advance towards the mastery
Meanwhile, Bowman has taken the job of night watch man, to enable himself to search for his sister though a bond they share, one night Bowman is approached by a hermit who reveals that Bowman has the power of the singer people, Power to destroy the mastery. Also Marius is announced as the Masters Heir
When the wedding party arrives they are treated to a gladiatorial like display. Then, when Sisi and Marius are to say their vows Sisi remains silent, finally shouting “No!” and retreating from the arena, the reason for Sisi's defiance is that she is in love with Bowman, after meeting him once. Marius himself was not overly disappointed by this turn, as he himself had fallen in love with Sisi's “Servant” Kestrel.
On this cue, Zohon ordered his soldiers to attack, the Mastery erupted into a panicked defence. Becoming coordinated as the Master, a corrupt Singer, exercised his will other the people. Bowman raced up to the masters tower, were they engaged in combat though use of the power of the singer people. When Kestrel and Marius also entered into the room the battle was being fought in, so far a deadlock, the battle took a drastic turn, the master ordered Marius to kill Kestrel, Marius resisted for barely a second before being swamped by the will of the master. Bowman couldn't stand by and watch his sister being killed, and called upon the power of Morah killing Marius and apparently killing the master.
Upon the masters collapse of power, the citizens of the mastery razed the city to the ground Zohon quickly regained control and declared himself ruler of the land. Removing Sisi's parents from power.
The entire Manth people left the city quickly, leaving with Sisi and her servant Lunki