Blue Penguin Classics edition mystery paperback

I lost my blue Penguin Classics mystery paperback yesterday around 3pm near the campus library on University Avenue in Carbondale, Southern Illinois. It's a mass-market paperback, about 320 pages, with a creased spine and a coffee ring on the front cover. Tucked inside is a tiny doodle of a lighthouse on page 92 and a red bookmark ribbon sticking out. This book was a gift from my aunt and has sentimental value; I'd really love to have it back.