THE NEXT DAY, ROGER came down from the malting floor in search of beer for Jamie and Ian, and found Brianna in Jamie’s office, writing.

She looked up at him, frowning, pencil in hand.

“How old is Pig Latin, do you know?”

“No idea. Why?” He looked over her shoulder at the page.

IMETAY RAVELERSTAY ANUALMAY: ONSERVATIONCAY OFWAY ASSMAY N NRG

“Time Traveler’s Manual?” he asked, looking at her sideways. She was flushed and had a deep line showing between her brows, neither of which detracted from her appeal.

She nodded, still frowning at the page.

“What we were talking about last night—it gave me a thought and I wanted to put it down before I lost it, but—”

“You don’t want to risk anybody stumbling over it and reading it,” he finished for her.

“Yep. But it still needs to be something the kids—or Jemmy, at least—can read, if necessary.”

“So tell me your valuable thought,” he suggested, and sat down, very slowly. He’d been working at the still with Jamie for the last three days, hauling bags of barley, then carrying the cases of rifles—Jamie had got another twenty, through the good offices of Scotchee Cameron—from their hiding place under the malting floor down to the stable-cave and finally unpacking and cleaning said rifles. He ached from neck to knees.

“So you don’t know anything about Pig Latin,” she said, eyeing him skeptically. “Do you remember what I told you about the principle of the conservation of mass?”

He closed his eyes and mimed writing on a blackboard.

“Matter is neither created nor destroyed,” he said, and opened his eyes. “That it?”

“Well done.” She patted his hand, then noticed its state: grimy and curled into a half fist, his fingers stiff from gripping the rough burlap bags. She pulled his hand into her lap, unfolded the fingers, and began to massage them.

“The whole formal thing says, ‘The law of conservation of mass states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as the system’s mass cannot change, so quantity can neither be added nor removed.’”

Roger’s eyes were half closed in a mingling of tiredness and ecstasy.

“God, that feels good.”

“Good. So what I’m thinking is this: time travelers definitely have mass, right? So if they’re moving from one time to another, does that mean the system is momentarily unbalanced in terms of mass? I mean, does 1780 have four hundred twenty-five more pounds of mass in it than it ought to have—and conversely, 1982 has four hundred twenty-five pounds too little?”

“Is that how much we weigh, all together?” Roger opened his eyes. “I’ve often thought the kids each weighed that much, all by themselves.”