That circuit is narrated by an Australian woman doctor, Sofia Raso, who has chosen to live and work in Afghanistan post-Taliban rule.

She lingers on each of the rituals and residents in the square, focusing especially on a tea-house where the oldest completed book in the world enjoyed a one-night stand (en route to the British Museum).

The introduction is extended, affectionate and intimate. Each character is treated seriously with generalisations pruned to a minimum. (Leith does compliment Afghans for dexterity in waiting and accepting.)

Shaahir Square works as a microcosm of a society and its setting, something like the way Egypt's Yacoubian building did for Alaa Al-Aswany or its Midaq Alley for Naguib Mahfouz.

Leaving aside The Kite Runner and - the much superior - A Fort of Nine Towers, modern Afghanistan has usually been a terrain for grim stories filled with dire facts rather than for literary fiction.

Nonetheless, detective novels can thrive in quite unlikely surrounds. Look at Colin Cotterill's poignant tales of the last coroner in Laos or Qiu Xiaolong's dramatic series about a beleaguered Shanghai police inspector.

Those who spurn books for screens would find "Baghdad Central" an intriguing detective tale set two countries away from Afghanistan.

With The Night Letters, Leith's plot takes off with a few actual letters, delivered at night, affixed to a door, containing what are taken to be unwarranted threats.

She uses her doctor heroine as a window into Afghan life, one able to experience - and pass judgment on - Islam, injustices suffered by women, death, meddling by foreigners and the persistence of hope.

Another intrusive expatriate supplies a love interest, sweetly revived. Crimes against children, hideously called "boy play", provide the spring for detection, drama and confrontations.

Leith does not overdo the dramatics. A vital police raid is mentioned rather than described.

The narrative, already gently paced, sometimes slows for extra explanations of characters' thoughts and feelings.

That said, Leith does take pains not to over-egg the plot, which concerns the alleged perfidy of an Afghan warlord turned politician.

Leith has done serious research into her fields of interest, and throughout accords Afghanistan and its people both sympathy and respect. An outsider should do no less.