“I’m sure they do,” she said, smiling, but unwilling to lose her train of thought. “And of course I’m making the assumption that the dimension of time is part of the definition of ‘system.’ Here, give me the other one.”

“It’s filthy, too.” It was, but she merely pulled a handkerchief from her bosom and wiped the mixture of grease and dirt from his fingers. “Why are your fingers so greasy?”

“If you’re sending something like a rifle across an ocean, you pack it in grease to keep the salt air and water from eroding it. Or guano dust getting into the mechanism.”

“Blessed Michael defend us,” she said, and despite the fact that she obviously meant it, he laughed at her Bostonian Gaelic accent.

“It’s all right,” he assured her, swallowing a yawn. “The rifles are safe. Go on with the conservation of mass; I’m fascinated.”

“Sure you are.” Her long, strong fingers probed and rubbed, pulling his joints and avoiding—for the most part—his blisters. “So—you remember Geillis’s grimoire, right? And the record she kept of bodies that were found in or near stone circles?”

That woke him up.

“I do.”

“Well. If you move a chunk of mass into a different time period, do you maybe have to balance that by removing a different chunk?”

He stared at her, and she looked back, still holding his hand, but no longer massaging it. Her eyes were steady, expectant.

“You’re saying that if someone comes through a—a portal—someone else from that time has to die, to keep the balance right?”

“Not exactly.” She resumed her massage, slower now. “Because even if they die, their mass is still there. I’m sort of thinking that maybe that’s what keeps them from passing through, though; they’re headed for a time that … that doesn’t have room for them, in terms of mass?”

“And … they can’t go through and that kills them?” There seemed something illogical in this, but his brain was in no condition to say what.

“Not that, exactly, either.” Brianna lifted her head, listening, but whatever she’d heard, the sound wasn’t repeated, and she went on, bending her head to peer into his palm. “Man, you have huge blisters. I hope they heal up by the ordination—everybody will be shaking your hand afterward. But think about it: most of the bodies in Geillis’s news clippings were unidentified, and mostly wearing odd clothes.”

He stared at her for a moment, then took his hand from hers and flexed it gingerly.

“So you think they came from somewhere—sometime—else, and got through the stones—but then died?”

“Or,” she said delicately, “they came from this time, but they knew where they were going. Or where they thought they were going, because plainly they didn’t make it there. So, you know …”