He had discovered a space capsule that had crashed in the mercury swamp two hundred years earlier. Ignoring the Second Doctor's warnings, he believed that the Daleks inside it could be used to serve the colony and help improve it, unaware that the Daleks were secretly planning to conquer it themselves.
He was shocked to learn of the Daleks' duplicity and had a nervous breakdown. Later, Lesterson distracted the Daleks long enough for the Doctor to overload the Daleks' power supply, although the action cost him his life. (TV: The Power of the Daleks)