smiley follows the clues to identify the real murderer, terence fielding, whom stella had been blackmailing over his wartime conviction of homosexual conduct with a member of the royal air force. the conviction was known to school authorities, who took advantage of the situation for their own ends with separate blackmail of fielding into remaining in his position at a significantly lower salary than his peers. perkins had inadvertently made a discovery that would derail fielding's attempt to implicate the husband and would have put suspicion on fielding himself. instead, until the end fielding maintained unawareness of the significance of what he had seen.