While exploring the planet Argo, Kirk and Spock are turned into water breathers.
The Enterprise and a Klingon ship must join forces to escape from a pocket universe that has been trapping starships for centuries.
The crew of the Enterprise finds themselves shrinking after being bathed with radiation.
The crew encounters Harry Mudd again, who is selling a fake love potion.
In orbit around a dead star, the Enterprise comes across a huge starship inhabited by a parasitic life form that threatens the entire ship.