“Theoretically, if Mesaana had this weave in force, she could have taken up the Oath Rod and sworn whatever she wished. ‘I vow that I will lie whenever I feel like it’ for instance. The Oath Rod would have bound her with that vow, but the weaves would have changed the sounds in the air as they passed her lips. We’d have heard her saying the proper oaths.”

Egwene gritted her teeth. She’d assumed that defeating the Oath Rod would be difficult. And yet here was a simple weave capable of the feat. She should have known—never use a boulder when a pebble will do, as her mother had often said.

“With this,” Egwene said, “they could have been slipping Darkfriends into the ranks of the Aes Sedai for years.”

“Unlikely,” Saerin said. “None of the Black sisters we captured knew of this weave. If they had, then they’d have tried to use it when we made them reswear the oaths. I suspect that if Mesaana does know this trick, she has kept it to herself. The usefulness of it would vanish once too many people became aware of it.”

“Still,” Egwene said. “What do we do? Knowing of the weave, we could probably find a way to check for it—but I doubt that the sisters would be willing to go through the reswearing process again.”

“And if it were to catch one of the Forsaken?” Yukiri asked. “It might be worth ruffling a few feathers to catch the fox hiding in the hen house.”

“She wouldn’t be caught,” Egwene said. “Besides, we don’t know if she’s using one of these methods. Seaine’s logic suggests that it might be possible—without too much trouble—to defeat the Oath Rod. The actual method Mesaana used is less important than the possibility of the act.”

Seaine glanced at Yukiri. None of the three had questioned Egwene’s knowledge that one of the Forsaken was in the White Tower, but she knew they’d been skeptical. Well, at least they now understood that it might be possible to defeat the Oath Rod.

“I want you to continue your work,” Egwene said. “You and the others were effective at capturing several Black sisters and unearthing the ferrets. This is much the same thing.” Merely far, far more dangerous.

“We’ll try, Mother,” Yukiri said. “But one sister among hundreds? One of the most crafty and evil creatures ever to have lived? I doubt she will leave many clues. Our investigations into the murders have, so far, yielded very little in the way of results.”

“Keep at it anyway,” Egwene said. “Saerin, what have you to report?”

“Tales, rumors and whispers, Mother,” Saerin said with a grimace. “You likely know the most famous stories regarding Mesaana—how she ran the schools in lands conquered by the Shadow during the War of Power. So far as I can tell, those legends are quite true. Marsim of Manetheren speaks of that in detail in her Annals of the Final Nights, and she’s often a reliable source. Alrom gathered quite a full report of living through one of those schools, and fragments of it have survived.