At oh, Bastien pauses his obedient following after Tiffany to look back at Arlyn, all polite curiosity.

"Why?"

Behind his quizzical smile, he's running through names. If it's a Riftwatcher he's referring to, there are only so many to consider. It's only a breath before he nods, face and posture both tightening—for Derrica's sake. For Tiffany's. To communicate to them that this is something to care about. He hadn't wanted to say we do have a problem before, having not ruled out Tiffany as the source of it, but now—

"Is that who sent the letters?"