Or at least, most of them believed this. One of the surviving doctors kept studying the results of the tests they’d run on the bodies, as well as the tests on the crew member who’d turned out to be inhuman, and she developed a theory. She believed an intangible creature had come aboard the Mull of Kintyre while the ship was traveling through the wormhole. It had tried to inhabit the body of a crew member, but this process involved some physical mutation, which had killed the host. It had moved onto another crew member and killed that one too. This process had been repeated over and over until the creature managed to latch onto someone who didn’t die, either because that person was physically different from the others or because the creature had learned from its earlier mistakes.

This doctor believed that if the creature could move from body to body, they couldn’t be absolutely certain it wasn’t still on board, hiding inside someone else. She insisted on running tests on every crew member but found nothing. The deaths stopped and the crew’s worries subsided. They focused instead on reaching their destination.

Yet the doctor never stopped worrying about it. Maybe the creature was learning—maybe now it knew how to trick the tests and pass for human. She wrote all this down, not just in her report that was stored in the ship’s systems but also on paper in case the systems failed. If she was right, it was too important to risk erasure. She didn’t tell a lot of people about it because she worried any of them might be the creature—but she did tell her wife.

As Iona read the document she remembered Dr. Hanna Bradley. This memory wasn’t vague and shapeless like the others that had drifted back to her—she saw Hanna’s face and remembered the room they had shared on the Mull of Kintyre and how it had felt to be with her.

Iona looked up at Victor and Alyssa, who had stayed with her while she read the last thing her wife had written.

“She died in the crash, we think,” Alyssa said, anticipating Iona’s question. “If it’s any consolation she was absolutely right. That report is an excellent piece of work.”

It was no consolation at all.

“We reckon the thing wanted to strand us here so it sabotaged the ship,” said Victor. “It wanted to cut us off from Earth.”

“Possibly,” said Alyssa. “Though it needs some of you alive, so if that was the plan it probably didn’t intend to kill quite so many of you.”

“How do you know so much about it?” asked Iona.

“This wasn’t the only colony ship to be affected. Dozens of ships that went through those wormholes came out with unwanted passengers. Most of them lurked undetected on colonies—”

“What are they? What do they want?”

“We call them the Poramutantur, and all they do is fight each other. They’ve been at it for thousands of years. And they’ll use anyone and anything as weapons. They inhabit the bodies of people with influence, they manipulate, they abuse trust—they set our colonies at war. Millions of people died. We’ve eliminated most of the Poramutantur now but it’s taken centuries to undo the damage.”