I Start Counting (1969), produced and directed by David Greene.
A teen girl has a big crush on her adult brother and begins having romantic delusions and erotic fantasies about him. She's adopted and a priest confirms this would not be actual incest, but still it is an awkward situation. I've read that unrelated children raised together tend to obey the incest taboos.
She begins to suspect that he is a local serial killer and plays girl detective. We suspect that such is her infatuation that she would not turn him in even if it were true.
As a thriller this is slow-boil with a lot of coming of age, slice of life, and on-location late 1960s ambiance. I was reminded of some other films:
And Soon the Darkness (1970): another slowly paced thriller. In both films we get to know a specific location very well: in that film a lonely stretch of French road, in this one a lane along the pond and the decrepit old house where the family once lived.
House (1977): a bizarre Japanese horror film staged as a girly adventure story. Like that, in this one the pop music and shopping content keeps us disoriented as to what kind of story we have.
The World of Henry Orient (1964): because of the friendship of two girls at an awkward age. Here they are a bit more advanced: in a competition for first sex (mostly lying about it) and covering for each other when out all night.
Some notable features:
Jenny Agutter fab club! This was two years before Walkabout (1971). She was 16, meant to be a couple of years younger.
Watch her laugh when she sees the nude pin-ups in her brother's shop. Embarrassed and excited at the same time.
The design exploits the youth vs age theme. The old buildings are being pulled down and the mystery house is dank and rotting, but the new apartment complex is clean and modern. The church is modern and its priest young and handsome. The girls live in a swinging 1960s world tailored just for them.
We have to have other suspects for the murders and have a good candidate early on.
In a plot twist fantasy and romance is drained from the story and our girl enters the adult world in a way she did not expect. She was in such a hurry and expected an exultant experience, but reality is something different.
Photographed by Alex Thomson -- Alien 3 (1992), Excalibur (1981), Legend (1985).
Available on Blu-ray from Fun City, associated with Vinegar Syndrome. I had never heard of the title before it appeared on disc.
Samm Deighan provides a valuable commentary track, with much to say about our character's sexual awakening, handled sensitively and without exploitation. She points out parallels and contrasts with Hitchcock's Shadow of a Doubt (1943).
She finds the modern apartment ugly, a step down from the old house.