The first time I stumbled upon Edith Tudor-Hart – a passing mention in an article about my grandfather, the double agent Kim Philby, which prompted me to hit Google – I was struck by a single image. It’s a haunting black-and-white portrait of a woman, her eerie gaze somehow at odds with the flapper-girl haircut, eyes pointed down as if distracted by something just out of view.

There is something simultaneously knowing and self-conscious about the figure as she sits back in her chair, arms crossed in a turtleneck jumper, a cigarette clutched between her fingers. Behind the eyes, there was something cool and unknowable but there was also something tragic, and – do I retrospectively fill this in, knowing what I know now? – a hint at the terror of what had already passed, and of what was still to come.

It seems impossible that I hadn’t heard of Edith until last year, given how much I’ve read about the lives of the Cambridge Spies. The story of the English gents who betrayed their country for the communist cause has been told time and time again. Yet rarely is there mention of the Vienna-born Edith Tudor-Hart – née Suschitzky – a figure so integral to the formation of the group that she was referred to under interrogation by Anthony Blunt as “the grandmother of us all”.

What I learnt as I continued to dig over the coming weeks and months, devouring what little I could find about Edith – not least through the fascinating documentary Tracking Edith, painstakingly created by her great-nephew Peter Jungk – is that she was the remarkably self-possessed and single-minded daughter of Wilhelm and Adelle Suschitzky, who ran one of the first socialist bookshops and publishers in a working-class district of Vienna. In 1934, with Parliament dissolved, trade unions forbidden and Vienna now an untenable place for Jews, Wilhelm shot himself in the bath.

A decade earlier, aged just 16, Edith had taken herself from Austria to England to train as a teacher under Maria Montessori. She later studied photography at the Bauhaus in Dessau, where her already fervent commitment to the communist cause was nurtured by her teacher there. By the time her father took his own life, in 1934, Edith was already working for Stalin’s secret police, the NKVD.

That same year, a few months after Wilhelm Suschitzky’s suicide, Edith recommended my grandfather, Kim Philby, be approached to work as a spy. She handed him over on a bench in Regent’s Park, where secret agent Arnold Deutsch delivered his pitch, inviting the connected and convinced Englishman who would become the reviled Third Man to work for the Soviets.

The story of what became of Kim and the other Cambridge Five spies, is well known. What is lesser known is what became of Edith.

For much of her life, she remained a committed spy. She also became a devoted single mother to her beloved son Tommy, who was a severely mentally disturbed child with various unconfirmed diagnoses, ranging from schizophrenia to severe autism. Alongside an impressive career as a photographer in advertising, to raise money to look after her only child, she spent years documenting the communist movement for the party as a photojournalist in Austria and the UK.

As well as a stunning portfolio of political photography, Edith’s contributions to the Soviet cause included handing over national secrets about the building of an atomic bomb – accessed via the Viennese nuclear physicist Engellebert Broda, with whom she had been having a romantic affair. She also acted as a conduit, passing on information from key spies including Anthony Blunt and Bob Stewart after the Rezidentura in the London embassy ceased activity, in the run-up to the Second World War.

In the early 1950s, when my grandfather first came under suspicion from British intelligence services – a decade before he was finally outed as a double agent and escaped to Moscow – Edith was driven mad by constant surveillance and interrogations at her St John’s Wood flat about her connections to Kim. She persistently denied their shared past and had managed to burn most of the negatives of her camera films that might connect the pair, in the sink of her home. But one photo – a now-famous image of young Philby, taken that summer in 1933, smoking a pipe – survived.

Though no link was ever proven, Edith was prevented from working as a photographer and, at the age of 44, she fled to Brighton where she opened an antique shop in the North Laine. She died 20 years later in a pauper’s hospice, her only child incarcerated in an asylum, her ashes scattered by an employee of the home, in the absence of family or friends.  Meanwhile she was effectively shunned by the Soviet regime to which she gave her life, without ever accepting a penny for her work. My grandfather, by contrast, was given an apartment by the KGB, as well as a state funeral in Moscow when he died there in 1988, and has since had a square dedicated to his name.

Having a long-time interest in espionage and spy fiction, I am fascinated by how women are cast in this predominantly male world – often relegated to bit-parts: lover, femme fatale, victim. Espionage is traditionally entrenched in the old boys’ network with new recruits scouted at Eton or Oxbridge, deals taking place in the darker recesses of gentlemen’s clubs across the world. With my first two novels – Part of the Family and A Double Life – I wanted to explore the idea of women who make seemingly unconscionable decisions, and how we react when they do. By shifting the narrative so that the woman takes centre stage, becoming the deceiver rather than the deceived, the traitor rather than the betrayed, an agent with agency in her own story, the lens through which we see everything about her is distorted. But Edith’s story is even stranger – and more intriguing – than any fiction.

As well as her significant connection to my grandfather, I feel a personal tie to Edith. I had no idea when I was a student at the University of Sussex that the tobacco shop where I bought smoking papers every week next door to one of my favourite bars was the same Georgian shop-front (still untouched apart from the signage) where, in the final years of her life, Edith ran her eponymous antique shop while living in the little room above, collecting jars and other curiosities, on Brighton’s Bond Street.

Her flat in St John’s Wood, where she was interrogated in her bed about her friendship with my grandfather, is a stone’s throw from my primary school. I drove past it every day for years, looking up at the windows and never imagining her face looking out, keeping watch for who might be watching her.

When her ashes were scattered, by an employee of the hospice where she died, they were tossed from a point on the Sussex Downs which is within spitting distance of the isolated college where I did my NCTJ studies in journalism some 40 years later. Edith’s footsteps are all over the streets that were most formative in my coming of age, and yet for so long I barely knew her name, let alone the significance of her story.

Today, Edith’s powerful photography, which ranges from images of working-class London life to demonstrations by unemployed Welsh miners, is still celebrated. Her photos can be seen as part of an online exhibition celebrating women refugee photographers, Another Eye, which ends on Saturday October 3. But her personal story remains largely untold.

In writing Edith and Kim, I hope to help return her to where she belongs – at the centre of her own story.

Edith and Kim by Charlotte Philby will be published in 2022