"It's a brilliantly dramatic period," she says. "We were still reeling from the Second World War and suddenly our friends became our enemies. But rather than the glamorous or seedy world of spying, I wanted to write from a more intimate perspective, about what happens in ordinary lives. To look at the people who aren't pulling the strings; who don't have power and control and could easily be victims."
In Exposure, Lily Callington is the doer of housework. She is a Jewish refugee who has created a small but happy post-war life in London with her husband Simon and their three children.
However, Simon has a secret in his past, a youthful love affair with a man called Giles Holloway who, unbeknown to him, is a Soviet agent. And when he does what seems to be an insignificant favour for Giles, it leads to him being suspected of spying and consequently imprisoned, leaving Lily to manage alone.
Trains are used as a motif in the book and comparisons have been drawn with Edith Nesbit's classic, The Railway Children. Dunmore admits the similarity but also points out a crucial difference.
"In The Railway Children you never know what is happening to the adults. The father disappears; the mother copes. Still I liked the idea of that structure and I wanted to tell a story about a family that is abruptly shattered."
Lily is the lynchpin of the family and the novel. To begin with she seems decent but dull.
"You think she's just a mother preoccupied with her home and children," agrees Dunmore. "But I want Lily to be constantly surprising you. She is under-estimated by everyone, a characteristic experience for women of that era, I think."
Dunmore's tendency to take a domestic view of events hasn't always been met with critical warmth. A previous novel about the siege of Leningrad was dubbed "a mum's-eye view" and "less Tolstoyan than suburban" by one critic. But she argues that the arena of home is a dynamic place for fiction.
"We're all intensely engaged with the home.
I can't think of a person who isn't. Home is a place where we think we are safe. So what more interesting thing to write about than when that safe space is threatened?"
While the actual espionage mostly takes place offstage, this is still a novel that seethes with secrets. "Everyone wants to sweep things under the carpet," says the author. "There is the shame and fear of exposure. And everyone in this novel is spying on someone else, even the children."
Dunmore tends to talk of the characters in her novels as if they are real. She has enormous compassion for them, even becoming attached to Giles, the spy and rotter, as she explored how trapped he was in his lies, although she is aware a lot of her readers won't feel the same way as they get to know him.
"That's the extraordinary thing about fiction," she says. "We only know a certain amount about the people in our lives, even our partners and children. But in fiction there is a lovely intimacy. You find out who they are when they're alone."
Now 63, Dunmore, who lives in England's West Country, has had a long writing career that also encompasses poetry, short stories and children's fiction. She didn't publish her first adult novel until age 40 and winning the inaugural Orange Prize for her third, A Spell In Winter, was what brought more widespread recognition. She still writes poetry because she can't imagine life without it and you can feel its influence in her prose, which is economical and evocative.
"Writing poetry is a good thing for a novelist because of the music and the way you hear language, particularly dialogue," she explains. "It also helps to have the habit of editing yourself pretty hard. I want to feel that every word is doing quite a lot."
Exposure, by Helen Dunmore (Hutchinson $37) is out now.
