Boris Johnson super-fan Nadine Dorries will publish a book settling scores over his downfall just three days before the Tories' annual conference.
The former Culture Secretary - who was named in a bombshell report for trying to undermine Parliament's Partygate probe - continues to maintain the ex-PM was wrongly removed.
She claims the "darkest political arts" run through the Tory Party.
Her book, named The Plot, is described as a "story of treachery and deceit". Ms Dorries received £20,500 as a partial advance from HarperCollins.
She claims to have discovered a "fault line" and a "history of deception" within the party as she takes aim at those she blames for Mr Johnson's removal.
It is likely to make uncomfortable reading for Mr Sunak, who Ms Dorries has repeatedly lambasted since her mentor's departure from No10. According to a statement released this morning, the book will tell how the "most charismatic politician of his generation" was "driven from office" and is supposedly based on the testimony of "dozens of inside sources".
Ms Dorries claims that "powerful, unaccountable forces behind the scenes" were behind Mr Johnson's downfall.
A statement by the publisher says: "This is a story of treachery and deceit at the heart of the Westminster machine fuelled by an obsessive pursuit of power which tears at the very fabric of our democracy."
Ms Dorries said: "When I started this book I had no idea of the journey I was embarking on. But the more people I spoke to in the heart of Westminster, the deeper the story unfolded. I had wanted to discover the forces behind the downfall of the Prime Minister.
"Instead, I found a fault line within the Conservative Party stretching back decades and a history of deception fuelled by the darkest political arts.
"If you thought power flowed from the people into Parliament, be prepared to think again."
Adam Humphrey, who negotiated the deal, said: "The Plot is an urgent look at how our government really operates, and I look forward to it adding to the current political discourse."
It will be released on September 28. Ms Dorries remains Mr Johnson's most steadfast ally, continuing to stand by him even after he was sanctioned for his Partygate lies and stepped down as an MP in a strop.
Last month she announced her own intention to quit as an MP with immediate effect, triggering a by-election, but is yet to formally do so.
In one recent attack on Mr Sunak after she was blocked from entering the House of Lords, Ms Dorries labelled the Prime Minister and his political aide James Forsyth "privileged posh boys".
She claimed she resigned as MP for Mid Bedfordshire after being "bullied" by No10 as she accused Rishi Sunak of "duplicitously and cruelly" blocking her from getting a peerage.
Ms Dorries used a TalkTV interview to launch a fresh attack on the PM, claiming he used "weasel words” and "sophistry" in a meeting with Mr Johnson which left the outgoing MP believing she would be included on his resignation honours list.
Ms Dorries sought to divide the row along class lines, branding ex-Winchester College pupil Mr Sunak and his old classmate James Forsyth - now his political aide - "privileged posh boys" who stopped her being offered a seat in the Lords.
"I'm broken-hearted, not just for me but for everyone who comes from a background like mine," she whined.
"This story is about a girl from Liverpool... who had something that was offered to her... removed by two privileged posh boys."
It comes after she was named in a report by the Privileges Committee on attempts to undermine the Partygate probe. It highlighted comments by eight Conservative politicians and claimed they were part of a co-ordinated attempt to undermine the panel's work.
Those named also included former cabinet ministers Sir Jacob Rees-Mogg and Dame Priti Patel.
