"Aag Ka Dariya" ("River of Fire"), her magnum opus, is a landmark novel that explores the vast sweep of time and history. It tells a story that moves from the fourth century BC to the post-Independence period in India and Pakistan, pausing at the many crucial epochs of history. Aag Ka Darya is essentially a novel written from the point of view of the believers of Pakistan and depicts their agony in detail, specially towards the climax of the novel. Aamer Hussein in The Times Literary Supplement wrote that "River of Fire" is to Urdu fiction what "One Hundred Years of Solitude" is to Hispanic literature. In a review for a 2019 reprint by New Directions Publishing, Aditi Sriram wrote in the New York Times that the novel "is as relevant in 2019 as it was when she first wrote it in 1959." Kamil Ahsan in The Nation wrote: "River of Fire tells a completist and syncretistic version of 2,500 years of history in modern-day India, Pakistan, and Bangladesh—beginning with the Nanda Dynasty on the brink of defeat by the founder of the Mauryan Empire (323 to 185 BCE), and ending in post-Partition despair.”