Mrs. Jeffries Rocks the Boat

Mirabelle Daws traveled all the way from Australia to Sheridan Square to visit her sister-only to die in the middle of a locked garden. All the residents of Sheridan Square have a key to the garden-but no one seemed to know that Mirabelle was planning to arrive. So the question facing Mrs. Jeffries is: who wanted to make sure that Mirabelle's visit was very, very short-lived?