Ooh, have you read Possession by A.S. Byatt? It's a long way from mindless beach reading, but it's got a grad student and a mystery and amazingly well rendered faux Victoriana. It's marvelous. There's also The Crimson Petal and the White by Michel Faber, which has Victorian hookers. And... hmm, I was always a big fan of Sue Grafton during my long-ago mystery phase.