Need a standalone mystery that I could hopefully find on Libby

Love a good mystery, but they all seem so dark lately. Ive read all Harry Bosch, some Elvis Cole, Anthony Horowitz's Hawthorne and Horowitz, and a myriad of others. Classics like Agatha Christie novels don't keep me entertained very easily, but I haven't given them a fair chance probably. I have recently re-read Lock In and Head On by John Scalzi and the sci-fi mystery was great, relatively low stakes. I also finished the Expanse Series which had overarching mystery….and to that end

Tired of series, just need a good standalone that I can hopefully find on Libby.

Thanks in advance