The Doctor pulled his screwdriver out and started to work on the vortex manipulator, needing a while to find the right settings. He wanted Jack to be well equipped, so what he was doing could pretty much count as an upgrade, too. Perhaps he was also showing off, because he couldn't resist. "Punch, no, but you should see me fence. But yeah. I'll bear that in mind, captain."

And then Jack asked about that and the Doctor's face hardened. He wished he hadn't drawn attention to it, because now he'd have to explain. But it was Jack's fate, Jack's life and he was free to talk and ask about it when he wanted to. Even Koschei. He couldn't keep him from everything.