On a visit to the planet Argo, the crew is attacked by a giant sea creature. When Spock and Kirk wake up from the attack, they discover that they are no longer able to breathe air, but now have gills and webbed fingers.
This is another average episode as Kirk and Spock try to discover a cure for their problems and are routinely mistaken as enemies with harmful intentions just like on almost every episode of Star Trek. As stated, this episode pretty much goes by the book when it comes to Trek episode. You already know how it will end before this episode really does start to begin. It is still a pretty good story that isn't boring, but it isn't a shocking episode that will leave you on the edge of your seat. Overall, pretty good, but could have been better.