Professor Quentin Quisling is a tertiary antagonist in the book The Falcon's Malteser and its film adaptation Just Ask For Diamond. Professor Quisling was famous back in the fifties or sixties, when he was around before computers. In the thirties, he designed computer fraud, which was a big joke because the computer hadn't then been invented. Professor Quisling designed many other things and may have had a hand in designing the Internet itself. But recently, Professor Quisling went missing. The police are surprised he hasn't shown up because he knew the Falcon, and knew where the diamonds were - the Professor built the safe that the diamonds went into. So, the police think the Professor is dead due to his absence.
However, Professor Quisling is not dead. He appears at the Diamonds' apartment, where he tries to do a deal with Nick Diamond for the location of the Maltesers. Nick gives the Professor a fake box of Maltesers, amazed that just because the Professor is an adult he thinks he can pull one over on him. But Nick aims to follow the Professor to the Maltesers and get the money himself.
Nick follows the Professor down the street but is suddenly knocked unconscious by Gott and Himmell. When he escapes from them and does them injury, the Professor and the Fat Man send thugs to capture Nick, and then the Professor expresses his anger that Nick tricked him. Just as the criminals are about to drown Nick, the police show up. The Professor and the Fat Man run to the boat, but the Professor is half-drunk and old, and he falls over into the river. Almost drowned, he has the misfortune to be sliced to death by the propellers.