She shook her head. “This was something generated within the Mind-set or the subsidiary substrate mechanisms of the Churkun itself. The ship had a one-off spy … you’d have to call it a program, it was so old and tiny; a virus, sitting in its computational matrix. Whatever it was – it deleted itself immediately – it had been in there since before the ship itself was constructed, while the Mind-set was still in virtual form, being test-run by the shipyard’s Technology and Processing Department, four hundred and seventy years ago. Even then, it might not have required anybody within the Tech Department to plant it; could be done from outside.”

“And it was doing nothing all that time?”

“Just waiting for something to come along sufficiently game-changing to be worth betraying its presence for.”

“And nobody found it?”

“Obviously.”

“Or nobody who wasn’t also a traitor, at least,” Banstegeyn said, glancing away.

The marshal frowned. “I think if we start assuming there might be traitors within the fleet’s virtual crews we make traitors of ourselves. Saboteurs, at the very least. This was something so small, in a set of substrates so vast, it was possible for it to hide. Once it was in there, no further—”

Banstegeyn’s eyes went wide. “What about the other ships?” he blurted.

The marshal sat back fractionally at being interrupted, but said, calmly, “All those still with us are checking. Now they have a rough idea what they’re looking for, it’s hoped they can either find anything similar or give themselves a clean bill of health within days.”

Banstegeyn was appalled. “Days?”

“Impossible to do any quicker. The fleet, such as it is, these days, remains fully operational in every other respect; the techs – the ships too – maintain there is absolutely zero possibility of anything similar taking over any part of the running of the vessels; stuff like this can watch and wait and signal if it finds a way, but it can’t affect.”

“And the Churkun?” Banstegeyn asked. “What’s it – is it returning to—?”

“The Churkun announced its determination to Sublime as soon as possible,” the marshal said. “Nothing more has been heard of it since so either it has already gone or it is still preparing to.” Chekwri smiled humourlessly. “I understand that the aftermath of battle, even a one-sided one, is not generally considered to constitute the most favourable condition for the instigation of Sublimation.” The pretended-at smile disappeared. “And kindly keep that secret, too, Septame. The ship didn’t announce this publicly and we’d rather people think it’s still with us; the fleet’s reduced enough as it is.”

Banstegeyn opened his mouth, seemed to catch himself, then said, “All right. Never mind. What about the Fourteenth?”

“We are almost certain—”

The septame held up one hand. “‘We’?”