While I attempted to work out such details, I thought again about “The City on the Edge of Forever,” and suddenly I realized something. In that episode, when McCoy leaps through the Guardian of Forever and changes Earth’s history from the twentieth century onward, he causes the alteration to the timeline by preventing the death of Edith Keeler. Miss Keeler subsequently founds a peace movement that delays the United States’s entry into World War II, which in turn allows Nazi Germany and its allies to capture the world. As a result, the remainder of the Enterprise landing party find themselves totally alone on the Guardian’s planet, with no ship circling in orbit above them and, as Spock notes, “with no past, no future.” But in the modified past, I asked myself, what had become of McCoy?

All at once, I saw that an entire period of the doctor’s life had been hiding in plain sight. Yes, his time in Earth’s altered past had occurred in an alternate reality that ultimately gets reset, erased by Kirk and Spock chasing him back to 1930 and foiling him from stopping Keeler’s death, but still, it had happened. If I wanted to investigate that time, I knew that I would need to do two things in order to make the story work for readers. First, I would have to find some means of having the events of McCoy’s “other” life inform his “real” life, and second, I would need to utilize that other life to help explain and then deal with his pattern of unsuccessful relationships.

From there, the details of the story at last came together. I would produce parallel narratives, one taking place in McCoy’s “present,” during the Enterprise’s five-year mission and afterward, and one in his alternate past, beginning with his arrival in New York City in 1930. A title even suggested itself fairly quickly: Provenance of Shadows-making reference to the origin of the dark side of McCoy’s life that had prevented him from finding happiness with a romantic partner.

Once I had finished beating out the plots and themes for the McCoy novel, I turned my attention to Spock. I at once found a starting point for his story late in McCoy’s life, at a time when I knew that the two characters would come together in Provenance. I immediately liked that, seeing how I could tie the books together. From the two-part Next Generation episode “Unification,” I knew that Spock’s last canonical appearance had him on Romulus, where he sought to further the cause of reintegrating the Vulcan and Romulan peoples, who had common forebears. I actually wrote a complete outline in relatively short order, putting together a highly complex political tale that employed elements of the first Crucible novel, the TNG episode in which Spock appeared, and the tenth Trek film, Nemesis. From a character point of view, it explored how and why reunification had become so important to Spock.

After sitting on the outline and mulling it over for a few days, though, I decided that I had made a mistake. Too much of the story took place in a time frame far beyond that of the TOS series and movies, and the study of Spock relied on his hopes for uniting the Vulcans and Romulans, an examination far less personal than would satisfy me. Consequently, I scrapped my ideas without ever even submitting the outline to my editor.

And so I began again, this time concentrating once more on the episodes of the Original Series and asking some of the same questions about Spock that I had posed to myself about McCoy. What didn’t I know about the character, and what would be worth discovering? I reviewed Spock’s arc, beginning with the earliest canonical experiences of his life-his birth, as depicted in The Final Frontier, and his near-death ordeal at the age of seven, as seen in the animated episode “Yesteryear”- through to his experiences as a Federation special envoy in the sixth film, The Undiscovered Country. To my satisfaction, I found something that didn’t quite scan for me, though I had never before thought about it. In Star Trek: The Motion Picture, it is revealed that, after the Enterprise’s five-year mission under Captain Kirk, Spock returned to Vulcan and sought to achieve the Kolinahr-the shedding of all emotion. I wanted to know why he had chosen to do that.

Now, I understood as well as any Trek fan that Spock has always considered himself Vulcan, not human, and that he subscribes to the lifestyle of the former and not the latter. He purports to control his emotions-a claim observably true in most cases-but it also seemed clear to me that he felt friendship for Kirk and McCoy, even if he rarely expressed himself in quite that way. Spock also appeared satisfied with his life. Why then had he elected to leave Starfleet, to leave his friends, and to endeavor to fully purge himself of emotion?

I thought about this for some time. The Motion Picture also revealed that Captain Kirk had been promoted after the end of the five-year mission to admiral, and posted to the position of chief of Starfleet Operations. Could that have motivated Spock to do what he’d done? That seemed unconvincing and not quite right to me. I couldn’t justify Spock’s resigning his commission and wanting to totally rid himself of emotion simply because his friend had moved on in his career.

Perhaps a traumatic event had befallen the first officer, I speculated. Because of their appearances in later films, I knew that both of his parents, Amanda and Sarek, were alive during the time frame in question, though The Next Generation would reveal their later demises. Surely Spock’s own death and then his rebirth in The Wrath of Khan and The Search for Spock, respectively, could be considered disturbing, but again, both had occurred after his decision to undergo the Kolinahr.

Since I could see nothing that would have reasonably impelled Spock to go back to Vulcan and try to completely eliminate his emotion, I wondered if I could develop that drive myself. But what form would that drive take? Once more, I looked to “The City on the Edge of Forever,” and again, that episode revealed something to me that I had never before realized.

When Kirk and Spock travel back in time through the Guardian of Forever in an attempt to avert the change McCoy made-or will make-to history, the first officer counsels his captain and friend that it is of paramount importance to restore-or maintain-the timeline. This appears quite clearly to be a core principle to Spock, one that he espoused quite plainly in an earlier first-season episode, “Tomorrow Is Yesterday.” It also seems reasonable: time and events have taken place, people have lived and died, and it would be unethical, perhaps even immoral, to alter those occurrences.

But then I considered the other occasions when Spock had traveled in time, and to my surprise, I saw that he had not always acted in concert with his professed convictions. In the animated episode “Yesteryear,” he intentionally alters the flow of history for the purpose of saving both his mother’s life and his own. And in The Voyage Home, he actually suggests plucking humpback whales from the past and bringing them into the future in order to attempt to save the population of Earth from an attacking alien probe. In both instances, though Spock possessed positive intentions which ultimately bore the fruits of his labors, he nevertheless violated the principle of striving to keep the timeline intact. He never appeared to consider doing so through the course of events in “The City on the Edge of Forever,” nor did he search for any means of sparing Captain Kirk the terrible loss of Edith Keeler. Perhaps he wouldn’t have been able to find a method of preserving the past without the death of Keeler, but he never even seemed to try.

This amounted to a subtle distinction in behavior, I knew, but one that I thought Spock and his acute, logical mind would discern. I also believed that Spock’s understanding of what he had done-acting in opposition to principle when it suited him, but having failed to do so when it would have most benefited his best friend-could prey on him, particularly when provoked to think about it during extreme circumstances. Such circumstances, I thought, might include Jim Kirk’s death.