7. Alien Parasite Attack!
Easily one of the greatest episodes of Star Trek: The Next Generation, Conspiracy featured a nasty race of alien parasites that infested Starfleet command and saw Picard and his crew facing down their own commanders in a race to stop the creatures taking over the Federation.
We like it so much, we even made the parasites one of our favourite Trek monsters a while ago.
How about exploring something similar with Kirk, Spock and the rest, allowing the filmmakers to explore corruption and illegal wars, Trek-style?
McCoy could get infected, forcing Kirk and Spock to try to save their - ironically ailing - doctor friend...
Drama, tension and weird beasts sprouting out of flesh. Trek does Alien!