At 53, Euphemia Sage, the protagonist of Fenwicke’s intriguing series launch, has an unusual reason to be anxious about the imminent arrival of menopause. A letter from her Aunt Maree, who looked out for her after Sage’s mother died when Sage was 16, to be opened on Sage’s 30th birthday, revealed an incredible secret. As “the eldest daughter of an eldest daughter of an eldest daughter going back many generations,” who has herself given birth to a daughter, Sage would be inheriting “Rachel’s Switch” at the onset of menopause. This would activate something in Sage’s genes, giving her unusual strength. A second letter, which arrived when Sage turned 40, contained another shocker—that her late mother, who she believed drowned accidentally, was murdered. Once Rachel’s Switch gets activated, Sage must deal with the kidnapping of her dog and an employee’s betrayal that puts Sage’s life at risk, even as she tries to adjust to having “speed, and enhanced senses,” as well as extra strength. Fenwicke’s intelligent characterization of her lead makes suspending disbelief easy. There’s plenty here to sustain multiple sequels. (Self-published)