Burnt Shadows, By Kamila Shamsie

At the core of Kamila Shamsie's new novel is the idea that an individual's identity is not a fixed block that can be slotted into an assigned square, but essentially liquid, evolving as life flows. Like water seeking its own level, Shamsie's characters – and there are many in this novel which has the sweep of a century and the scale of the planet – blend into new surroundings, maintaining their humanity. They are victims of forces larger than themselves: those who emerge are, in the end, not triumphant; they have survived.

Yet those with the power to send aeroplanes into skyscrapers, drop bombs that can wipe out cities, or draw borders between people to create new nations see individuals in a dehumanised form: as parts of groups they hate, be it by religion or nationality. Their decisions tear apart countless lives.

Burnt Shadows has many such people, drawn from Japan, Germany, Britain, America, India, Pakistan and Afghanistan. These individuals lead global lives even before globalisation became a buzzword; their ethnicity, language and nationality are mere accidents of birth. A seminal event, not fate, casts their lives across the globe. The novel celebrates how they cling to inner selves in spite of displaced lives.

There is Hiroko Tanaka, daughter of a "traitor" father, who hates Japan's militarism. She must atone by working in an arms factory even though Japan is losing the war. She speaks German and translates for Konrad Weiss, who has come to Nagasaki because his half-sister Ilse and brother-in-law James Burton would rather not have a German relative with them in colonial Delhi while world war rages in Europe.

When the atomic bomb is dropped "to save American lives", Konrad perishes. But Hiroko survives, bearing the scars of the bomb on her back. Shamsie describes in achingly moving prose the incineration of the city, and the melting of Hiroko's skin, the scars clinging to her back forming permanent, unfeeling shadows, like black birds.

Hiroko seizes the opportunity to leave for India, and turns up at the Burtons' home, unsure of what to expect. Ilse – who is now Elizabeth – warms to her. Hiroko begins learning Urdu from Sajjad Ashraf, a young Indian Muslim and legal apprentice of Burton. Inevitably, they fall in love, despite the Burtons' initial misgivings.

The threat of Partition is ever-present, and though Sajjad does not want to leave India, the Burtons convince him, sending him to Turkey until the violence subsides. However, India won't let him back because they left during the Partition, and reluctantly the Ashrafs move to Karachi, with Sajjad as a mohajir: the not-endearing term for refugees from India.

The novel turns darker: Raza, the Ashrafs' son, a misfit among pure Pakistanis ("Pak" in Pakistan means pure), makes friends with Afghan refugees. Hiroko and Sajjad welcome Harry Burton, Ilse's son, to their home. It is 1983; Harry is now an American, as Ilse has left James for the US. Ostensibly a consular officer, his real job is to help the mujahideen against the Soviets in Afghanistan. The plot moves inevitably towards 9/11, at a quickened pace, with edgier, less lyrical language, hurtling to an end at Guantanamo Bay, where no norms apply.

Shamsie's challenge is to build the architecture through strong characters without letting the burden of history crush the structure. In Hiroko, she has created just such a character. Some of the minor characters aren't always capable of bearing that burden. They remain true to the message Shamsie conveys – of the common humanity of our interwoven lives. But the pace compresses them. Shamsie has squeezed a violent century's universe into a ball, and rolled it forward with an overwhelming question: Why?