10 Star Trek Episodes That Started As Something Completely Different
3. Dear Doctor
Dear Doctor is an early episode of Enterprise, in which the ship comes into contact with a planet that contains two species living in a kind of harmony. They are the Valakians and the Menk, with the former being the more advanced of the two. However, they are stricken with an illness that they have not been able to find a cure for, so they ask Archer for Warp Drive technology to allow them to seek their own resolution.
The episode ends with the revelation that the Valakians aren't sick - they are all dying due to a flaw in their DNA. They have reached the end of their evolution, with the Menk now destined to become the dominant species on the planet. Phlox reveals to Archer that he has a cure, though Archer decides not to help them, believing it is not their place to alter the natural development of a planet.
In the original version of the story, Phlox still finds the cure, but he keeps it to himself. This, actor John Billingsley believed, was a crucial part of his development as a character. It was Phlox's convictions, over Archer's insistence, that means the Valakians didn't receive the cure. The network demanded the ending be changed as, in Billingsley's opinion, they simply wanted the crew to be in place to support Archer.