Jessie Burton on her new novel The Confession

Faced with a room full of pictures of breasts, the novelist Jessie Burton and I are laughing nervously.

We are at the Cindy Sherman retrospective at the National Portrait Gallery, trying to be mature in the Sex Pictures Room. Burton, who trained as an actor, wanted to see this exhibition because she is interested in the roles people assume. “It’s about how we change our images,” she says. “And how easy it is in a way to inhabit other roles.”

We have a Sherman debrief in the gallery café and Burton tells me about her third novel, The Confession, published last month. It’s about 35-year-old Londoner Rose Simmons, who works in a coffee shop and is feeling trapped in a long-term relationship. Her boyfriend, Joe, is happy following his dream (running a Mexican street-food business called Joerrittos) but his enthusiasm only makes her feel more restless.

Then her father reveals that her mother, who disappeared when she was a baby, used to go out with a famous female author, Constance Holden. At the peak of her success Constance became a recluse. Rose tracks her down and tries to find out what happened to her mother. “Much of the book is about hitting certain milestones or not, and not knowing what that means,” says Burton, 37. “Be it having children, your relationship, your career ... There is this idea that at 30 you might have life sorted. Life isn’t like that, and that’s OK.”

The book explores motherhood from different angles. Rose’s best friend, Kelly, is an Instagram influencer whose daughter is the star of her social media feed. “I wanted a positive portrayal of a woman in her mid-thirties and a positive portrayal of motherhood,” Burton explains. “I know motherhood can be really hard, I see from my friends that it can be thankless as much as it is life-affirming. I wanted in Kelly to create someone who is just dealing with the good and the bad times.”