Two things are noteworthy about The Venetian Affair. One was that Robert Vaughn tried to break out into the big screen like such television contemporaries as James Garner and Steve McQueen without the success that they had. The second was that this was the last film Boris Karloff did that was not related to the horror genre.
The film begins with a bang. An American diplomat is given a bomb and it detonates in a disarmament conference in Venice. No one can figure out why, but you can bet the USA does not want to be held responsible when forensics prove it was our guy who was the suicide bomber.
Our man in Venice for the CIA Edward Asner sends for former agent Robert Vaughn who is now an alcoholic newspaperman working for a wire service. They suspect his ex-wife Elke Sommer has something to do with it and he's the best at finding her. She's also the reason that he's no longer with the CIA.
Boris Karloff plays an elderly man of geopolitical mystery. He knows what's going on, but some sinister folks are controlling him.
The Venetian Affair is a pedestrian affair moving at a paint drying pace and Vaughn after being television's urbane Napoleon Solo in The Man From UNCLE never quite got his teeth in this part. Karl Boehm is a good villain and only at the very end do we find out who he is working for. As for the reason why the diplomat did the foul deed, that you watch The Venetian Affair for.