"YES! Brilliant, yes! Definitely found you," The Doctor had been meticulously analyzing the data collected from the vicinity sweep and was able to gleen traces the alien parasite. He had also done a few tests on himself and found that his strange, instantaneous fear had been the result of some kind of attack from the creature. A secretion, gas, or psychic field perhaps. "That means...," The Doctor shuddered making a noise of revulsion as he shook his head. The dangerous alien had been near enough to dose him; It had probably been right behind him.
"Hold on, how am I supposed to get close it if I keep turning tail and running? There's gotta be something. There's always something, oh!" He piped as the screen blipped with new data. The Doctor scrambled around the TARDIS flight panel, flipping levers and pulling switches, making a full trip around the panel back to the screen. He took out his black-rimmed glasses and read aloud. "This species emits a psychic pulse that induces fear in its prey. Must be a pretty strong telepath to The only known defense against the fear is to have a stronger emotion directly associated with the alien. A stronger emotion? Like what? Love? Hate? Yes, of course! Oh yes!"
The Doctor cut the celebration of this information short. It was invaluable, but how could he develop an emotion, a strong emotion, for a being he had never met personally? He could find another person who met the requirements, but what good what it do? Someone who had survived an encounter with such a creature would want nothing to do with it. Even if they did, the individual would probably get killed as the Doctor was running away in terror. The last thing the Doctor needed was another death on his conscience.
"What about a synthesized emotion, ah nope." the Doctor located the note in the file that labeled artificial emotions as 'ineffective.' What was there left? What could he do? This creature was killing and possibly converting innocent people if the parasite had mutated further. The Doctor had to do something.
"Alright, what about a memory implant? No, wouldn't work. Damn!" He was familiar with several technologies that altered or implanted memories, but none to date had ever worked on him. A Time Lord's mind was too complex for any of the memory devices he knew of. It would be like pinning up a sketch of a stick man in a collection of well-loved and familiar painting and trying to pass it off as an original.
"Oh," he said quietly, coming to the idea that he had been shoving to the back of his mind for hours now. "I could implant the memory if...I guess...it's the only way." He reached into his jacket pocket and pulled out an intricately carved silver pocket watch.
The next morning he rented a storage space in a small city about 20 miles from Golly and parked the TARDIS inside. He knew what he was about to do was beyond dangerous and would most likely end up with him being killed, or worse infected, but the Doctor knew that he was the only one who could stop this creature. A nagging voice in his head kept telling him that his life was worth more than a few humans. Humans died every day and he couldn't save them all. He could be doing so much more right now instead of chasing an elusive monster that would probably kill him.
"No," he told the voice, "I have to try."
He took one last look around, then activated a button that began to lower a device from the ceiling of the TARDIS. The Chameleon Arch. He had used it not long before when he had to become human in order to hide from a dangerous family of aliens. The situation had played out, though not without an unforgivable amount of devastation to innocent people and people he loved. At least that time, he had had Martha to watch out for him. This time he had no one.