It was a day after the abortion of the invasion of Vulcan before Commander Sela thought to review her automatic security tapes. Picard, Spock and the android had been locked in her office for some time before they escaped. If they had said anything useful it might go better for her at the trial - which is to say she might survive, perhaps even with her family name intact. To Sela's disconcert, she found that - once the android had set to work on the holoemitter - she herself was the subject of discussion.
She learned that Picard had accepted her contention that her existence was his responsibility, though she hadn't told him the whole story. But he hadn't done so on her word. Sela wondered who this Guinan was, to have such influence over Picard (and over Spock too when Picard had repeated Guinan's opinion), and yet be unknown to Sela. She also wondered how Guinan came by the information, since he or she obviously hadn't told Picard any more than Sela had. That suggested Guinan didn't know the whole story - but then how did Guinan know as much as was said?
Picard and Spock spoke of pursuing the matter as a temporal investigation led by, of all people, Picard's chief medical officer. Then the android announced the completion of his sabotage, and the Federation officers' conversation ceased as they assumed their holographic hiding places. Sela switched the recording off, having no care to live through the subsequent events another time.
What would that hag Pulaski know about temporal mechanics? No, she was back at Starfleet Medical now, and Crusher was back on the Enterprise. Even more unlikely.
Wait - Picard had said it'd been since before the House of Duras debacle that he'd met with with the doctor he and Spock had discussed but not named. Could they have been referring to - what was his name - McCoy, who'd served with Spock? Simple longevity didn't itself confer expertise in time travel, though with the experiences rumored of these two while they served under Kirk ...
Of course the Federationese title "doctor" was applied most commonly to medical professionals, but not exclusively. It could signify an excess of education in any field. Spock held the equivalent of many "doctrates" though he had never formalized any.
So. An engineer or scientist, a specialist in temporal mechanics. Not serving the Federation in any official capacity. Contact with Starfleet or the Enterprise infrequent, apparently unpredictable and uncontrollable. Known to both Spock and Picard; so well known that his or her proper name need not be mentioned between them. ... Or whose proper name was not known. At that thought Sela's heart seemed to stop.
Learned scientist. Name not known.
Time travel.
Could it be that the Alchemist was known to these Federation men?
END OF PROLOGUE