I think bits of the plot came first—or at least, ideas and images that eventually became a plot. But the characters started forming at the same time, really. As soon as I have an idea for a scene or a storyline I can’t help imagining a character inside it: What kind of person would be in that situation, why, who are they? With The Downstairs Neighbor I kept adding in more and more voices as the story took shape—there were times I despaired of keeping track of all their plots and timelines and backstories! I loved writing the different characters, though, and knotting their lives together. None of them are based wholly on people I know, but of course elements creep in that are influenced by real people, or aspects of myself: Emma’s compulsive sketching and antisocial hamster, Kate’s introversion and love of English, Paul and Freya’s competitive sportiness . . .

The converted Georgian home where all of the characters live feels so vivid! Is it based on a real place? Why did you choose to locate all of the characters in one building?

The house became more important with each draft. I wanted a suburban setting, so I based it in Kingston upon Thames, where my sister used to live. At first I pictured my sister’s building as I was writing (she lived in a ground floor flat like my character Emma—though she has pink hair, not blue!), but as the plot became bigger, so did the house, and I ended up with a tall Georgian townhouse, a bit like the one my mum and dad live in. Once I’d moved all the key characters in together, the story got more intense and claustrophobic, which I loved. It was fun to be able to picture the three families on their three different floors. It meant I could keep cranking up the tension in the building as their lives started to intertwine.

What was the research process for The Downstairs Neighbor? Did any surprises come up while you did research for the novel?

I admit I don’t enjoy researching as much as writing! Many of my former colleagues at the University of Birmingham were incredibly patient, thorough researchers, but I’m afraid I’m not! I write first, research later, which sometimes means going back and correcting things. However, I love it when the research throws up further ideas for the story, which it often does. And when the writing takes me down bizarre research trails, into topics I never thought I would need to know so much about. The two storylines that required the most research—without giving anything away—were Paul’s and Kate’s. There were some elements of those that were unfamiliar and slightly complicated. I take full responsibility for any errors!

The story is narrated from several different perspectives—were there any sections that you particularly loved writing, or that were more challenging than others?