For instance, this is how her chapter on Rajiv Gandhi begins: “ ‘Rajiv, if you can’t convince me about this Muslim women’s bill, how are you going to convince the country?’ Sonia said to her husband.” Even more inviting is the opening sentence of the chapter on Narasimha Rao. “ ‘I heard you were doing Puja after 12 o’clock on 6 December,’ Nikhil Chakravartty, a Left-leaning journalist said to former Prime Minister (PM) PV Narasimha Rao.” With that sort of start it’s impossible not to read on.

Now, Chowdhury’s book doesn’t present great revelations that will make you rethink your view of any of the six PMs. This is not a reappraisal. But it has stories, quotations and a vast quantity of research that fleshes out and adds detail to what you already know. Her book helps you understand things better.

Her comments on Rao are particularly engrossing. First, there’s her understanding of the man. “Rao … was given to having arguments with himself. He would internally debate an issue and see both points of view to such an extent that no clear picture emerged,” she writes.

Chowdhury says Rao didn’t want a majority in 1996 — and he didn’t get one either — because then he would have to give way to Sonia Gandhi. “Rao had a better chance of becoming PM again only if the Congress was in a minority.” She’s right, but this hadn’t occurred to me earlier.

It’s Rao’s relationship with Atal Bihari Vajpayee that transfixed my attention. “They went back a long way — and had come to each other’s rescue at critical moments in their careers.”

In October 1995, at the United Nations General Assembly, Vajpayee was seated between Rao and Bhuvnesh Chaturvedi, a junior minister. Chowdhury quotes Chaturvedi: “Vajpayee leaned across and said to Rao, ‘Kalyan Singh humare bahut virodh maen hai, unko nahi banna chahiye (Kalyan Singh has been opposing me, he should not take over as CM of UP)’.”

That evening, Chaturvedi asked Rao whether they should help Vajpayee. “Haan keh do Voraji ko (Yes, tell Voraji to do what’s necessary),” was the reply. Vora was the governor of Uttar Pradesh.

The message was delivered and Kalyan Singh did not become chief minister (CM). Chowdhury’s explanation couldn’t be more telling. “The installation of Kalyan Singh as the CM in Lucknow would mean power moving into the hands of Advani. This could create problems for Vajpayee ... Rao understood the importance of UP for Vajpayee — and decided to help his friend.”

Five years later, Vajpayee apparently returned the favour. In September 2000, a trial court held Rao guilty of bribing Members of Parliament to defeat a no-confidence motion. “Rao sought Vajpayee’s help to close the case,” Chowdhury writes. “Chaturvedi told me that he was the go between. ‘I went to see Atal ji’, Chaturvedi recalled. ‘He called Brajesh into the room’. He told him, ‘Isko khatam keejiyee’ (close this matter).”

In March 2002, the Delhi high court acquitted Rao. “It was significant that the Vajpayee government decided not to appeal the high court verdict,” Chowdhury adds. “Instead, CBI decided to drop the case.”

In all my years, I haven’t come across a story like this. They were opponents. They fought for the same job. Yet, they helped each other get out of scrapes or nip challenges in the bud. This is a classic case of you-scratch-my-back-and-I’ll-scratch-yours. Neither emerges smelling of ittar. I wonder how their parties will respond?

Karan Thapar is the author of Devil’s Advocate: The Untold Story. The views expressed are personal