Manil Suri's ambitious new novel brings together an unusual love triangle, a religio-racial Mumbai apocalypse and an action thriller. "Brings together" seems more accurate than "blends", since the elements fight each other more than they get along. The opening is narrated by Sarita, separated from her husband Karun at a time of political crisis and social meltdown. The first thing she does is to buy a pomegranate, at an exorbitant price, and defends her possession of it with a devotion that seems excessive even when it is revealed that she used it in the past (following a tip from The Kama Sutra) to amplify Karun's rather muted sexual interest.

India has been invaded by China, its troops pouring through the northeastern frontier, and then by Pakistan. The UN forced the withdrawal of China (acting in concert with Pakistan all along), but Pakistan stayed put. Then cyber-attacks disabled many institutions, including computer networks, so that mobile phones and the internet packed up. In these circumstances, with nuclear warfare looming, no reaction can be described as normal, but fixation on the powers of fruit is a hard one to share.

The thriller aspect has been well plotted, but its horrific aspects must be downplayed if the romantic triangle is to remain the focus. Set pieces become sketchy and even massacres arouse little reaction. Providential turns of event reliably rescue the main characters, as if this was a romp, though, not a comedy.

Sarita's narrative alternates with contributions from a Muslim man named Ijaz ("Jaz" or "the Jazter"). Jaz too is obsessed with finding Karun, and shadows Sarita across Mumbai, intent on following her clues and getting to him first. He's an ex-lover of Karun's, rejected after he reverted to his previous type and was unfaithful.

Indian homosexuality is enough of a taboo subject that it's bracing to read about Jaz's happy days of cruising in Hyderabad, where he would never know what language his partners might use at the moment of orgasm, quite possibly Urdu or Telegu or a mix of both ("only the techies came in English"). Yet the sexual psychology is always thin. It's not just that Jaz is an amoral predator redeemed by his love for a nice physicist, it's that his amoral predation was accompanied by an unwavering commitment, however frantic the carnal context, to safe sex. Here Manil Suri seems to be backing away, presumably to avoid reinforcing negative stereotypes, from the destructiveness that is just as much a part of homosexuality as of heterosexuality. Snooky, the incongruous lady-boy Muslim (and terrorist fellow-traveller) narrator of Timothy Mo's recent Pure, is a much more complex creation, and much more alive.

Karun is hardly even a sketch for a character. His attraction for Sarita is bound up with "the passivity at the core of his being, his need to be a conduit", but for the reader he seems closer to a blank. When Sarita refers to him as "the third vertex in our triangle", it seems all too accurate. He's part of a design not a drama.

There's a rather self-conscious passage early in the book in which Karun lectures Sarita on the Trimurti, the Hindu trinity of Vishnu, Shiva and Brahma, representing forces of preservation, destruction and creation. It's self-conscious because Karun, who proposes substituting Devi for Brahma, does so in a novel with Devi in its title by an author whose previous novels are The Death of Vishnu and The Age of Shiva. This mechanism serves to neutralise the most interesting element in the book by offering a symbolic resolution, with forces balanced "as evenly as the particles in an atom", a new trinity combining male and female, Muslim and Hindu, gay and straight. Readers of The City of Devi are encouraged to look beyond the sordid details, like queasy museum visitors being reassured by the curator that apparently pornographic sculpture really only represents the harmony of the cosmos.

Stanley Kubrick's celebrated 1964 satire on the atomic bomb, Dr Strangelove, famously ends with the eponymous character stepping out of a wheelchair, thrilled that he can suddenly walk. As he does so, mushroom clouds erupt to the romantic strains of "We'll Meet Again". The Mumbai depicted in Manil Suri's third novel swells under the promise of nuclear attack with the same mixture of bombast, absurdity and yearning. To this, add the melodrama of Bollywood, the vicious theatricality of organised religion, the carnality of a love that dare not speak its name, and you have a devilish, enjoyable carousel of a novel.

Sarita and Jaz are two people in search of their lost lovers. Although she is a statistician, the impending apocalypse has made Sarita superstitious  she carries a pomegranate in the folds of her sari, which she hopes will lead her back to the man she loves before Pakistan fulfils its threat to push the nuclear button. Meanwhile, the city trembles from the force of the massacres within. Muslim babies are beheaded at Haji Ali mosque by Hindu extremists. Elsewhere, people are being hunted, burned and beaten in the name of religious purity.

The personal politics of lust run in tandem with the grand geopolitical narrative. At the heart of the novel lies a snake pit of titillation and predation. "The Jazter", as he refers to himself, is dedicated to his chosen pastime: "shikari", or "game-hunting". A child of international academics, he woos men from different backgrounds for casual sex in the parks, baths, toilets and cinemas of countries all over the world. When he finally falls in love, and finds himself getting sentimental, he wonders which hole he is trying to fill. Literal and metaphorical are conjoined to powerful effect.

This method of portrayal is less successful for Sarita. Like the Jazter, she objectifies the man she loves  gazing upon his body with a hunger that seems too forced and unilateral at times to be convincingly sustained. When she begins the long path towards gradual consummation, the reversal of expected gender roles required by her character also sits awkwardly: an otherwise indifferent kiss from her beloved is described as so electrifying that it "left the muscles in my throat engorged and took away my breath".

Suri writes with a cinematic bravado and humour that is very appealing. A child from the slums, chosen for deification due to her second set of arms (a birth defect that causes some to believe she is a reincarnation of the many-armed Devi goddess), commands crowds of thousands with the aid of hidden stage pyrotechnics. When things stop going her way, she reverts to her eight-year-old self and pounces on one of her disciples with feral anger, biting into his neck. The crowd surge upon seeing the blood, running to offer up their necks in turn for a lucky, blessed bite.

Similarly, historical tropes are used in fast and loose fashion, to wonderfully subversive effect. Bollywood meets the Bible and the Kama Sutra  a burning train careers off its tracks and into Jaz's home so that he can meet Sarita and begin his quest; illicit lovers run in front of bullets for one another, and find themselves creating a new holy trinity in bed. Their threesome  a beast with three backs  results in a semi-virginal conception.

Despite the official name change in 1995, the city is often referred to as Bombay, dancing under its secular name with two fingers raised to Shiv Sena, the rightwing Hindu nationalist party that pushed for it to be renamed Mumbai. The use of both names contributes to the dualism that forms the repeating pattern of the book. When Jaz tracks down his long-lost cousin Rahim, the man who first initiated him into the ways of shikari through nude wrestling in their late teens, he finds him as a transvestite running a luxurious hotel in the Muslim enclave of Mahim, who refers to herself as "Auntie". Rahim mocks Jaz for his liberal naivety and vague attempts at nationalism. "Well let me tell you, my flag-waving Jazmine, while you were swilling beer and chocolate with the American and Swiss, I was being bottle-fed the Indian dream. Nehru and Gandhi  the whole secular ideal. So what if our government perpetrated years of carnage against its own citizens in Kashmir? Or systematically filtered Muslims out from its armed forces and police regiments. Or turned a blind eye each time the Hindus decided to here and there roast a few minorities alive?'

This interweaving of personal and political significance means that The City of Devi is not subsumed by anger or the horrors that it describes. Instead, there is always room for exuberance and slapstick as this consuming, passionate, and ultimately poignant story hurtles to its conclusion.

 Nikita Lalwani's novel The Village is published by Viking.