An evil eye - Jason Goodwin

When the body of a Russian agent is found down a monastery well, Yashim
knows exactly who to blame. Fevzi Ahmet Pasha, commander of the Ottoman
fleet.

Years ago, when Yashim first entered the sultan's service,
Fevzi Ahmet was his mentor. Ruthless, cruel, and - in Yashim's eyes -
ultimately ineffective, he is the only man who makes him afraid. And
now Yashim must confront the secret that Fevzi Pasha has been keeping
all these years, a secret whose roots lie deep in the tortured
atmosphere of the sultan's harem, where normal rules are suspended, and
women can simply disappear.

Once again, Yashim and his friends encounter treachery and politics, played out against the backdrop of 1840s Istanbul.