I am looking for a film from my childhood. Years 55-80 from last century.

It was a film in the style of detective and crime movies, somewhat reminiscent of the atmosphere of the film 'How to Steal a Million' starring Audrey Hepburn and Peter O'Toole. The film I'm looking for also featured a pair of main characters - a woman and a man. The main character's car was driving along a road through a forest, leading to a hidden residential building in the forest, perhaps resembling a mansion. The protagonist drove to that place at least twice. On one occasion, there was a dry tree with protruding roots lying across the road near the mansion, but on another occasion, the tree was not there. It was a puzzle for the main character. Later, it turned out that the tree could be mechanically lowered using an electric mechanism, and a key was needed to lower and raise the tree. The protagonist arrived at the mansion twice. Once, there was a lively gathering inside, possibly a secret meeting of a clandestine organization. Our hero observed the meeting from outside through a window, and it seems he was caught while doing so. On the second visit, the mansion turned out to be abandoned, neglected, cluttered, dusty, with cobwebs, like an old attic. This was also a mystery for our hero - why the mansion was lively with people talking on one occasion, and on another occasion, it resembled an abandoned, neglected attic. Towards the end, there was a car chase during which someone crashed into the lowering tree with protruding roots, resulting in a tragic accident. This film was also in the style of the movie "Charade" from 1963. I'm not sure if it was a standalone film or an episode of a series, like, for example, "The Avengers."