The Vulcan captain sat at his work desk in the corner and steepled his fingers. “As you are aware, Jim, we had not been able to determine a single common factor among the previous systems struck by vacuum flares. Though they were all visited by the Enterprise in reverse sequence, and all contain relatively advanced worlds in regular contact with the Federation, the list excluded numerous worlds that fit those same parameters. Therefore, any hope of predicting future flares relies upon identifying some additional variable shared only by those systems. Yet the ones we could discern appeared trivial: all entailed layovers of several days, all entailed vessel maintenance and resupply, all entailed shore leave for at least a portion of the crew.”

“All routine matters.” Kirk stopped there, resisting the impulse to insist that Spock get to his point. He knew Spock well enough by now to understand that the captain wished to restate the parameters of the problem clearly as the first stage of his methodical analysis.

“So it would seem,” Spock said, “but that creates a dangerous temptation to dismiss data that could be significant. Consider, Jim: Though the Enterprise is the unifying variable in all these incidents, the vacuum flares appear to be aimed instead, however imperfectly, at the planets the ship visited—never at any point in interstellar space, even ones where the Enterprise spent a considerable amount of time.

“It stands to reason, therefore, that the key lies with something that occurred on those planets while the Enterprise visited them.”

“I see what you’re getting at, Spock.” Kirk began to pace the room. “If some… cosmic force is sending these flares… then it’s not targeting the ship, but one or more of its crew. Somebody who left the ship at each of those ports, and did something to attract its attention.”

“Or did something that triggered some form of natural outburst as a delayed reaction,” Spock countered. “It is still too early to make assumptions regarding the causal factor; I am merely proposing a correlation.”

“Of course. But it does narrow it down. It’s not about the Enterprise, but about the people aboard her.” He snapped his fingers and pointed. “That’s why the Deltan system is significant. The Enterprise didn’t go there, but one of the crew did.”

Spock nodded. “Upon having this insight, I reviewed the duty rosters to compile a list of personnel who went ashore at every one of the systems affected by the flares. I was able to narrow it down to eleven people, including you and myself, but no further.”

“How many had previously visited Delta?”

“Within a year prior to the Enterprise’s visit to Vega Colony, records show only two.” He worked his console, bringing up a personnel file displaying a familiar square-jawed face. “Lieutenant Vincent DeSalle made a layover in the system in late 2265, only long enough for a brief sightseeing tour.”