Blood and Circuses by Kerry Greenwood

Phryne Fisher is bored. Life appears to be too easy, too perfect. Her household is ordered, her love life is pleasant, the weather is fine. And then a man from her past arrives at the door. It is Alan Lee from the carnival. Alan and his friends want her to investigate strange happenings at Farrell's Circus, where animals have been poisoned and ropes sabotaged. Mr. Christopher has been found with his throat cut in Mrs. Witherspoon's irreproachable boarding house and Miss Parkes, an ex-performer, is charged with his murder.