"I really wanted them to all have a really strong motive to murder," Lucy Foley told us of The Guest List. 

Her latest whodunnit takes place off the coast of Connemara, as people gather for the glamorous wedding of Jules Keegan and Will Slater: an invitation to die for - and a weekend that the guests will never forget. As the festivities of the weekend go on, happy families are torn apart by hidden jealousies; old friends find past grudges coming to light again. And the wedding cake has barely been cut when one of the guests is found dead. The storm continues to unleash its fury on the island, leaving all the guests trapped with a murder amongst them. And the author spoke to Her about the killer surprise of who turned out to be the murderer, why she decided to set the book off the coast of Connemara and what she's working on next. "I went into it thinking it would be one person [who would be the killer], and then about a third of the way into writing I thought it would work so much better if [the person who ended up being the killer] had done it," she explained. "All that stuff that I was coming up  with about various people's backstories, I thought there was a way to bring that person's story [to the forefront]. It suddenly struck me, and I got goosebumps when I thought of it - it as so exciting, and it seemed to work so much better. "I think as a writer, you have to leave room for those moments when it happens. You plan really carefully, and with this sort of book, that's so important - it's like a puzzle. But you have to leave room for the curveballs, the things that excite you. I think that's where some of the best twists come in." And while The Guest List is set off the coast of Connemara, it turns out it wasn't always meant to be that way. "When I had the very first idea for this book, it was the wedding that came [to me first]. I knew that I wanted to set it on an island, and my first idea was that I was going to set it on a Greek island - mainly because I wanted to go there on a research trip," she said with a laugh. "But as I started to think about it, it felt so wrong. Because there's a wedding and a murder mystery, the whole format has an innate kind of campness to it. You have to have some kind of darkness to offset that, and the location can work really hard and do that for you." However, she said that things started to feel a little too 'Mamma Mia!' with the wedding taking place on the Greek island, noting: "A wedding on a Greek island, where's the darkness going to come from?" She recalled how the "whole book kind of found its shape" after she and her husband spent a long weekend away in Ireland. "I'd been to Connemara a lot, I traveled there a lot when I was a kid. My grandfather originally came from there  and my dad spent all his childhood summers there. I went there a lot as a child, and I went back there with my husband for a long weekend and we stayed in Ballynahinch which was amazing," she coninued. "We got the ferry out to Inisbofin and it was standing there - it's such a dramatic place, it's so beautiful but the weather and the elements and feel quite hostile. I thought, this was the perfect place, the perfect contrast to the glamorous wedding that Jules is trying to throw. I felt it could almost become a character in the novel, where it started to bend the human visitors to its whims in a way." Both The Hunting Party and The Guest List are being adapted for the screen, with a screenplay - and a lead actress - in the works for The Hunting Party's adaptation. "[The Guest List] adaptation is a long way down the road, they're doing The Hunting Party first - it's really exciting. I genuinely thought that we would sell the option, and then never hear anything ever again because I've heard of that happening so many times," the author told us. "But they're really on it. They've got a screenplay written for The Hunting Party and they've got a lead actress attached who would be perfect as Miranda. But then they've got The Guest List as well, a kind of second series. They've got the TV/film rights, so it's not that they definitely won't make a film - it's just they're focusing on TV. "They're talking about a Big Little Lies type format, each one would be about an hour; high production value and quite glossy. Each [season]  would be six to ten episodes, I think." After three historical fiction novels, it was an idea that had been "niggling" at her for a while that sparked her move towards writing thrillers and murder mysteries. "I'm loving writing thrillers. I'm fascinated by people, and this gives me a great chance to explore that - and people's hidden secrets and darkness and what's going on under the surface. I think it was a thing of trying to write the book that I wanted to read. I had this idea niggling at me for awhile, that I wanted to read a modern take on Agatha Christie - that classic, closed room setup. And then I was like, 'well, I could just have a go at writing it myself',"she explained. "That's how [the move into thrillers] came about. It was a funny one because I didn't want to tell my editor; I didn't think she'd necessarily want me to go off and take things in a different direction. It was like a bit of a side hustle, writing historicals - editing the final one - while writing The Hunting Party on the side. It was like a secret project." She also shared a little bit about what fans can expect from her third novel - and why it's "slightly different" than The Hunting Party and The Guest List.  "The Hunting Party and The Guest List are like sister books, they're both set in similar remote locations and they're a similar demographic of people, I guess you could say. The third book is slightly different. It's still the classic murder mystery format, but it is set in a beautiful apartment block in Paris - one of those ones where it's around a courtyard, so you can see into other apartments. It's a bit Rear Window in that sense," she explained. "All of the suspects in the murder are people who live in the block. We've got the elderly lady with her little dog, some students, the hot guy who lives in the basement flat, this very glamorous couple who throw parties for all the neighbours. They're all implicated in some way, and they've all got a big secret tying them together."

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• The Guest List by Lucy Foley, published by Harper Collins, is available in stores now.