Ripper begins with a brutal murder and a roomful of elementary school students. So yeah, you might call the book — Isabel Allende’s first murder mystery — a bit of a departure for a novelist who’s perhaps best known for mannered historical fiction and finely wrought family drama. But that’s not to say it reads like anything less than Allende (who’ll read this week at First Congregational Church of Oakland, 2501 Harrison St.) at her best — even if it is, admittedly, much, much creepier than, say, Daughter of Fortune. Ripper, which follows a precocious but lonely teenage girl as she investigates a string of murders in and around San Francisco, is expertly paced, gorgeously written, and, most of all, surprisingly fun — gruesome murders and all. She’ll be joined in conversation by San Francisco Poet Laureate Alejandro Murgia.