Detective fiction has produced its fair share of idiosyncratic heroes, but Yashim, the enigmatic protagonist of Jason Goodwin's debut novel, has to be the first eunuch detective.

Set in early 19th-century Istanbul, The Janissary Tree is a complex and often frustrating mystery story. A concubine has been murdered in the sultan's harem and a young soldier has been found dead inside a giant cauldron. Asked to investigate, Yashim soon discovers the deaths are connected. Goodwin has previously produced an acclaimed history of the Ottoman empire, Lords of the Horizons, and the historical detail can't be faulted, but there is something severely lacking at the centre of his novel. It simply doesn't work as a thriller, the narrative is too convoluted and the sense of suspense is negligible.

There are the seeds of something fascinating here. As a eunuch, Yashim is able to operate outside regimented Ottoman society, to associate with women and to infiltrate forbidden places in the city; he has a near-invisibility that makes him an ideal detective. Unfortunately, the potential brilliance of this idea is often lost amid Goodwin's cluttered prose and some uneasy shifts in style. Caught between a historical novel and a thriller, The Janissary Tree works as neither.