Star Trek IV: The Voyage Home
Star Trek IV: The Voyage Home is the fourth film in a hexalogy.
But it’s often considered the third film in a trilogy-within-a-series, beginning with Wrath of Khan. It’s even sold this way in some box sets.
If we can say crap like “Last Crusade is the third movie in a trilogy,” we can isolate trilogies within longer series.
Hey, wait a second…how many movies are in the Star Wars series now…?