The Perfect Body - Professor Molly Mysteries, #8

It's one thing to invite your toxic ex to drop dead. It's quite another when he takes you up on it. It's Professor Molly's first night out since her baby arrived. She's thrilled to accompany Donnie to Mahina State University's exclusive donor dinner. Unfortunately, she and Donnie are assigned to the same table as Stephen Park, Molly's insufferable ex. While Stephen and Donnie exchange (un)pleasantries, Stephen's new girlfriend helpfully lectures Molly about losing her pregnancy weight.
Needing a respite, Molly ducks out to the ladies' room...a decision that puts her in exactly the wrong place at the wrong time, and entangles her in a murder.