At first, as Kate scrubbed her face, leaving Tony ruminating on nothing new, he pressed his lips together with his own annoyance; Kate's frustration was familiar to him and should have been old news as he tried to work beyond it, not be forced to stew in it with someone else. That was why he locked the door. He had to remind himself that Kate was new to this situation and was due her frustration still and to try to be more sympathetic or they wouldn't get anywhere. After all, it was so familiar.
Kate's important, if belated, nugget of information helped, too. Tony's eyebrows rose in surprise and seventy queries rushed for his attention at once, tripping over themselves. Even if Cassie had a hundred friends-and-suspects, the S.H.I.E.L.D. agent would top the list. Who else might need her to rush off at a moment's notice for something dark and secret? "Why didn't you say that first?" Tony accused, then remembered: sympathetic. "I'll call the Director," he offered in a softer tone, both hands on the table like he might physically reach out to her in lieu of being emotionally approachable. "But I bet you're on the money," he said. As far as Tony was concerned, those kind of facts barely needed confirmation; it was whatever else Nick could reveal about this other girl that would be helpful. It couldn't be a S.H.I.E.L.D. problem, though-- why ask Cassie and not deal with that in house? Why ask Cassie and not someone more seasoned and reliable? Maybe he couldn't ask Nick. If a S.H.I.E.L.D. agent was going rogue, any accomplices might have been in enough shit without Tony directly implicating them, however pure the motives were.
Tony had been staring, unseeing, at his hands and hoped with very little optimism that he hadn't been talking to himself when he caught himself in his stupor. Shaking himself out of it, he reached for his coffee again to chase away any more of the same, then tentatively asked, "Cassie wouldn't do anything...?" What was the language for something like that? Tony's gaze darted, searching for the right word, but it didn't come to him. 'Bad' wasn't right, she was adamantly just. 'Stupid' was probably too right, but not entirely applicable.