Work Like a Charm - Martin Cate

Amanda Clarke knows she's a witch. She unleashed unstoppable magic to save her friends and catch a murderer. 
But she only did it the one time. And now? Back to powerlessness.
Her friends insist that all she needs is proper training. Sophie wakes her before dawn for meditation and workouts designed to channel magic. Brianna buries her under books, so many books.
Amanda longs for a distraction. But when the woman who lives next door to Miss Zenobia Weekes' Charm School for Exceptional Young Ladies turns up dead, and the murder weapon dates back to Prohibition, she gets more of a distraction than she bargained for.
But who in 1927 would want her neighbor dead in 2018?