Ianto is grateful for the out that John gives him. Not that he doesn't appreciate TJ's curiosity, but that he's not certain Jack's immortality is really his secret to tell. Especially when Jack didn't even tell Ianto himself about it, and he had had to find out the hard way after months of working beside the other man and worrying for him every time he'd put his life in harm's way, not knowing that even if he'd died he would still come back anyway.

"You know Torchwood," Ianto replies. "The alien and the weird. Anyway, he's the only one to really understand it well, since he ran off only a few days after that. Maybe if he shows up around here one of these days you can ask him," he suggests. Which is in truth a terrible idea, but its in his opinion much better than him answering now.

Speaking of those diagrams. "I've got a question for you two then. Who or what is this SGC? I'm guessing that's. Who you work for, at least?" Maybe.