Dr. Morelle investigates

the long version

"When Brian Cartwright receives a death threat, he calls in the famous criminologist Dr. Morelle to protect him. Apparently, he is to die at nine pm that same day. So with Cartwright alone, locked inside his study - windows and doors sealed - Dr. Morelle waits in an adjoining room, also locked ... Yet when Dr. Morelle re-enters the study afterwards, he finds Cartwright's body slumped on his desk, shot neatly through the head - and not by his own hand!"--Publisher description.