I'm a sucker for a boarding school setting. 'Truly Devious' by Maureen Johnson is a must. It's set at Ellingham Academy, a private school for gifted students, which was founded with a murderous mystery that's never been solved. The protagonist, Stevie, is a true crime enthusiast there to crack the cold case, but a present-day murder pulls her in. The secrets span decades, connecting past and present students and teachers. The scandals are academic, artistic, and deeply personal. It's a trilogy (plus more) that rewards patience, with a wonderfully quirky cast and a lush, immersive atmosphere. The high school here is a character itself, full of hidden tunnels and tragic history.