Miss McGuire is Missing by Eileen Robertson
I met the author at the novelists' conference earlier this year, and bought this, her first novel from her.
It's a unusual and great read - a thriller where the main characters are retired. Miss McGuire is an elderly ex-school teacher who goes missing while on a pensioners' mystery coach trip. Ben , wife Rosa and her sister Anna decide to investigate, and go back to the pub where she was last seen. Ben ends up getting kidnapped, and the two women, with the help of the pub landlady, need to find him and rescue him. Meanwhile the pub landlord is seriously ill and the dodgy local doctor looks like he's trying to bump him off...
There are some quite sinister undertones to this book, although it reads like a light-hearted romp through middle England. There are more twists and turns than the country roads through which the mystery coach tour passes. The book is unusual because of its main characters and because of the imaginative plot. Very readable - I couldn't put it down. It may seem expensive on Amazon as a hardback Robert Hale publication - I'd urge you to go find it in your local library.