Well, this is my version of Gary Mitchell and the Star Trek XII
The story begin shortly after the end of Star Trek XI. The Enterprise is ordered to bring the Vulcan Survivor to planet Alpha (just named it). At the same time, McCoy has an invitation to attend the Federation Medical Conference in Beta Planet (just named it). With him, the doctor bring his old friend, a beautiful female Doctor who also get an invitation from the medical conference Organizer.
This female doctor bring her special patient, an eight years old boy named Gary Mitchell who suffer an incurable unknown desease that can't be cured by the most modern medical technique at that era. She hoped that the other doctors have a medical method to save the boy.
Well, because the female doctor is beautiful, Kirk is agree to bring them to the conference planet without thinking. he, of course has his own agenda with the female doctor.
After bring the Vulcan to their new planet, the Enterprise get a distress call from a cargo ship that attacked by a pirate ship. Although there are another ships in the region, Kirk decide to help the merchant ship in order to show off to his new female friend.
The merchant is no other than Henry Mudd. His ship is broken beyond repair, but him and his cargo is safe. The merchant ask Kirk to bring him along in the enterprise to the beta Planet. Spock tell Kirk to refuse the merchant's plea; but the female doctor insist that Kirk should help Henry Mudd and bring him along with them.
No one know that Henry Mudd bring a dangerous cargo with him. When the pirates attack them again, the cargo is leaking and spread dangerous virus to the ship. Everyone get infected. This is the reason why Kirk hates Henry Mudd so much. The only one who still healthy is Spock.
McCoy and the female Doctor do their best to save the crews from the disease. But, this virus is not the only thing that the Enterprise must face. The pirate come again to get the cargo. So when Kirk and the other crews fights against the pirate, McCoy and the female doctor fights against the Virus.
Because of the lack of healthy crews, the Enterprise can't match the pirate ships. In no time this ship is boarded by the enemies. In order to survive, Kirk, Sulu, and Chekov organize the crews to fight the enemy.
At this moment, Spock find that Gary Mitchell is becoming healthy again. Not only that, this boy has become an adult in just several hour after the virus spread. He, then advice McCoy to use the Gary's blood as antibiotic. With this new serum, the crews are saved from the death.
It is not only that, Gary obtain a strange godly power. With his new body. He saved the enterprise by kicking out the pirates from the ship.