Murder in Williamstown by Kerry Greenwood

The Honourable Miss Phryne Fisher is up to her elegant eyebrows in mystery once again!

Awakening unusually early one morning, Phryne Fisher finds herself with a rare stretch of free time to fill. After dropping her daughters off for their school-sponsored charity work at the Blind Institute, she visits a university professor whose acquaintance she'd made—and admired—on a prior case. At lunch, the smitten professor invites Phryne to dine at his home in Williamstown later that week. 

Bookending her pleasant dinner with her new friend Jeoffrey, Phryne makes two disturbing discoveries: first, a discarded opium pipe in the park, and later the body of a Chinese man on the beach—cause of death not apparent, yet ultimately ruled a homicide. Shortly thereafter, the teenaged sister-in-law of Phryne's longtime lover Lin Chung disappears from her home. But when one of Jeoffrey's colleagues is murdered in front of a houseful of guests at a Chinese-themed party he is hosting, Phryne can't help but wonder—are the incidents all related somehow? And who on earth has been leaving notes in her letterbox, warning her to "REPENT" and that "THE WAGES OF SIN IS DEATH"—?

In addition to the formidable and fashionable Phryne, this clever mystery once again features Phryne's three wards with their own mysteries to solve: Ruth and Jane, tracking an embezzler at the Institute, and Tinker, whose help Phryne enlists to uncover the author of the threatening missives.