Jack watched Koschei moving about erratically and sighed, locking eyes with the Doctor. Was he really just going to trust him like that? "Whatever you did... I'm sure he's grateful... but you also have to know that whatever you did to fix him can be undone... and if he finds out that you've messed with inside his head? It'd be the end of you. What were you thinking?"

Jack looked very, very serious, and perhaps a touch scared. If the Master woke up, he'd no doubt kill him and then take the TARDIS to a place he could kill everything else, too. "This was not a good idea."