Paolo Cavara had already directed an earlier giallo by the time he made Plot of Fear. His previous effort - The Black Belly of the Tarantula - was pretty much a textbook example of the genre. By 1976 the sub-genre had ran its course and that may be why Plot of Fear tries to bring in a few different angles into the giallo template. For this reason it's a relatively distinctive effort. For my money it isn't as good as the classic-style Tarantula. It lacks the thrills of that one. Nevertheless, it remains a worthy effort.
Rather than a completely new take on the genre, it might be truer to say that Plot of Fear mixes typical giallo aspects with atypical ones. We have traditional giallo elements like a group of unsympathetic rich people being violently murdered one by one, a secret sex club, dark secrets from the past informing the present and each murder being signatured with a page from a sinister sounding children's story book (in this case a book called 'Shock-Headed Peter). As you could also gather the plot-line is typically convoluted too. Where things deviate from the norm is the inclusion of paranoid thriller material, no doubt influenced by the Watergate fallout that shaped many other films of the time. This is in reference to the whole wire-tapping/tapes thread and the morality of the private investigators whose services can be bought. The film overall does seem to have at least some social and political conscious, which is very far removed from most gialli. Its mystery is also wrapped up in a somewhat unorthodox manner that is significantly different to others in the genre.
The casting is a little unusual too for a giallo. While John Steiner was a regular at playing shady characters in these types of movies, the same cannot be said for the American actors Eli Wallach or Tom Skerrit. The latter has a very minor role indeed, almost irrelevant; you almost wonder why they didn't just hire one of their stock bit player actors for his role. As a film, this is a pretty decent effort. It isn't as formulaic as most in the genre. While it's central mystery is intriguing enough and builds up interest by way use of some interesting flashbacks. One of which shows the rich and decadent clique relaxing while watching a pornographic cartoon. I really would like to know what it is, as it looked like a bit of a riot. Answers on a postcard for that one.
Overall, Plot of Fear isn't among the best in the giallo genre. But it is probably among that grouping of titles that straddle other genres and are somewhat less predictable. Not essential stuff by any means but fans of Italian genre pictures will surely find something to enjoy in it.