Blue paperback mystery novel with torn spine

I lost my blue paperback mystery novel yesterday around 3pm near the Fort Gratiot Lighthouse parking lot along the St. Clair River in Port Huron. It's a mass-market paperback, about 320 pages, with a visibly worn spine and a blue ribbon bookmark peeking out. On the back cover there's a small library sticker with a faded barcode, and inside I tucked a pressed concert ticket from last summer—the paper is curling at the edges. This book also has sentimental value; it was a gift from my aunt who loved mysteries, and I really need it back.