Everyone’s favorite crime-solving senior citizens return in The Last Devil to Die, the fourth installment of the Thursday Murder Club series set in a U.K. retirement home. Author Richard Osman, who is also the host of the British quiz show Richard Osman’s House of Games, shares details about his beloved characters and an upcoming film adaptation. BY ELIZABETH HELD

The Thursday Murder Club members are ex-spy Elizabeth, former psychiatrist Ibrahim, Joyce, a former nurse, and Ron, a one-time union activist. How did you create these four distinct characters?

I love unusual gangs, people with different skills and from different words. I knew I wanted four people that came from different directions. Everyone in Britain is obsessed with class. Our entire society is based on whether you were born working class or middle class. I wanted two women and two men, and two working-class characters and two middle-class characters.

Then, I think it is the four quarters of my brain. Ron is a trade union activist who’s very belligerent. There’s a bit of me in that when I get angry at the television or on social media, I feel my inner Ron come out. There’s Ibrahim, who was a psychiatrist and is very rational. He’s putting lists together, likes everything in order and laminates everything. That’s a big bit of me as well. And then Joyce and Elizabeth, who are sort of the leaders; Elizabeth is extraordinarily competent and has led an extraordinary life. Joyce is essentially my mum. She’s the quiet one who actually gets all the work done. For a writer, it’s lovely to be able to write in different voices.

You continue to explore dementia and its effects on patients and their families in this latest book. Why was it important for you to include that?

As the population ages, I think there are very few families who are completely untouched by it. It’s such a cruel illness because to lose one’s mind, to lose one’s sense of self is so extraordinarily debilitating. And everyone deals with it in different ways. I know with my grandparents, it’s a loss. It’s a loss while somebody is still there, which is an extraordinary thing to go through because you can still hug somebody, but you can’t speak about something that happened 10 years ago.

It’s something I really wanted to explore because it is about love, life and who we are as human beings. You can see from the book everybody has different opinions on dementia and what it means and what should be done. So, I wanted to write