"Diplomatic Passport" is a crime thriller that is too slow-paced and implausible to be of any real interest. While the plot has a couple of good ideas, and the acting is not bad, there are too many other defects that bring it down. The story concerns a diplomat and his wife who arrive in London, only to become enmeshed in a long series of inexplicable, annoying, and occasionally frightening events. They have to figure out what is going on, while trying to extricate themselves from some difficult situations. It's the kind of plot that in better hands could make a good story, but it does not come off very well here.
One major problem is that it moves far too slowly. There are long parts of the film showing the couple settling into their hotel room, ordering food, making telephone calls, and so forth - rather than building up suspense, it just gets boring. Most of these scenes are not worth watching in themselves, either, with the exception of a mildly humorous scene when the diplomat is in France and tries to explain to a French cook what it means to cook an egg "sunny side up".
The story is also too implausible to be taken seriously or to create any sustained suspense. The explanation for everything is not very satisfying, and the characters make too many obviously bad or irrational decisions, even allowing for their stress.
Marsha Hunt is fairly good as the diplomat's wife, especially considering that her character's actions are often not very believable. And the rest of the cast is mostly alright, given that their characters are routine. But there is just not enough here to make the film of serious interest.