The Troubled Spirit (1974)

dan mateo conducts paranormal experiments in the botanical section of alpha and an unsuspected mental symbiosis with plants produces incredible results: a disfigured being appears and kills several times. bergman, thanks to a session, manages to discover that it is the same mateo returned to the past to avenge his death. dan is upset and, at koenig's request, lends himself to act as bait to lure his ghost into a trap and destroy it; but the temporal circle is destined to close.