Five Go Mad in Dorset (1982)

In the 1950s, four children, Anne, described as a 'proper little housewife', the rather butch George who has an unhealthy relationship with her dog Timmy and their brothers Dick and Julian, whose relationship seems to be more than fraternal, go on a cycling holiday in Dorset where their flair for detection - plus their snobbery and xenophobia - gets a whole string of suspicious characters arrested.

Unfortunately the movie Five Go Mad in Dorset is not yet available on HBO Max.