Freedom Seeker (1971)

Starring Patrick Macnee, Peter Cushing, Alex Davion, Johnny Sekka, Madeleine Hinde
Directed by Michael Burrowes
(actor & director credits courtesy IMDB.com)

An investigator follows a missing Oxford student to Greece, where he finds he's been caught up in a mysterious cult involved with a series of murders.

Also identified under the titles Blood Suckers and Incense For The Damned, this is an unusual film to classify, as it starts out as sort of an adventure thriller, and then a psychedelic exploitation story, before transforming into an all-out horror film in its final half hour.  There's a good cast, and although Macnee and Cushing play smaller roles than their billing would suggest, the young leads like Davion and Sekka perform well and offer engaging characters.  Overall, I thought the picture was diverting and enjoyable, with beautiful Greek scenery and an interesting score by Bobby Richards that alternates between symphonics and funk, although the film is marred by some poorly lit night scenes, as well as scenes of exploitation that really aren't necessary.  IMDB credits the direction to Robert Hartford-Davis, using Michael Burrowes as a pseudonym.