Detective Abigail Cartwright has earned a reputation for solving weird homicide cases, but, when she's called to a lecture hall at the local university, she faces the oddest one yet. During a What If ... lecture, run by soon-to-be-retired Professor Gertrude Milligan, two students died. Without any signs of how or why.

Confused, Abby digs in to solve the mystery, only to find several old cases connect—or do they? Were the two students murdered, or was something else going on?

Professor Leon Wellington is worried about his aunt Gertie. Their personal history was bad enough, but to have two of her favorite students die right in front of her has left her shocked and grieving. How can she not be a prime suspect in this case? Then she goes missing ...

When the past collides with the present, the stakes are higher than ever, as a killer realizes how close he is to losing everything ...