Book 20 in the Psychic Vision series.
What If ...
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...