In the 16th century, it is not unusual for slave markets of exotic countries to swell with numbers of white-skinned captives culled from raids on the English coast and shipwrecks of foreign vessels, the market of the wealthy men who covet pale beauties with blue eyes growing.

In 1599 Istanbul, the new sultan, with the aid of his mother, the Valide Sultana, cultivates an assortment of such women - the lighter the better, all the more valuable. The variety of women in the harem is already impressive, a heady mix of multi-hued ladies who hold the sultan as the center of their universe.

Residing in the harem for only two years, Celia Lamprey is such a girl, one remaining shipboard friend by her side as they adapt to the foreign ways of their changed fortunes. In the harem, every movement is watched, every action suspicious, various factions vying for power and position in the sultan’s favor.

An English merchant ship has just pulled into port in Istanbul, delivering an elaborate invention - part clock, part musical instrument - as a gift to the sultan to cement trading concessions. Unfortunately, the item is damaged in transit; while it is repaired, Paul Pindar, secretary to the English ambassador, learns that his fiancé, whom he thought dead, is alive, espied in the heart of the harem.

Paul despairs, realizing Celia will never be allowed to leave, belonging now exclusively to the sultan. But he cannot bear to think she might know he is so close yet unable to rescue her. Although Paul plots with the help of a servant and an impressive local astronomer, he is thwarted at every turn. The Valide Sultana performs her own political machinations, aligned with the Chief Black Eunuch and one of the “three Nightingales of Manisa” in a deadly struggle.

In modern-day Oxford, advanced student Elizabeth discovers a fragment of a letter that leads her directly into Celia Lamprey’s story. Fascinated by the possible fate of this young Englishwoman sold into slavery so many years before and herself running from an unhappy affair, Elizabeth travels to Istanbul, where she undertakes a thorough search of historical documents that may yield clues to Celia’s fate.

Finding the distraction she craves, Elizabeth applies for study in Istanbul, building her doctoral dissertation on the adventures of the merchant seamen and Celia’s Lamprey’s time in the country. Did she escape? Was her fiancé able to save her from a lifetime of seclusion?

The information she unearths leads Elizabeth to Celia’s truncated existence in the harem, a last opportunity to make contact with her love through the Aviary Gate and the mysterious world of the harem where the trivialities of the outside world cease to exist. Celia’s story becomes Elizabeth’s mission, a compelling counterpoint to her own emotional evolution.

• The Pindar Diamond
• Courtesans: Money, Sex and Fame in the Nineteenth Century