sentences:  The Doctor and his companions are taken captive and trained up by the robots as the replacement crew members, however only three additional crew members are required, so the member of the Doctor's party that proves least useful is to be callously killed off by the human crew.This was Holmes first story submission for the series, and was primarily rejected due to the robots role being similar to that of the Mechanoids in "The Chase" from the previous season.Holmes would later resubmit this story idea to producer Peter Bryant on 20 May 1968 which led to the commissioning of what would become "The Krotons".