[ A mixture of the Doctor's own hubris and the principle by which he tries to live compelled him to appease the incorporeal creature crying out for help. Rationally, perhaps, he should have known better, but who better to assist than a Time Lord with powerful mental defenses? He couldn't have predicted exactly how it would feel—though he's no stranger to having other beings in his mind, some quite malicious—but this entity has asked for help, not taken it by force. And he's the Doctor; he can handle it, better than anyone. Were the spirit left crying out for sanctuary, there was the risk as well it might possess someone far less capable. This is the better way, and he'll be able to expel it easily.
The moment he agrees, the Other that settles into his mind feels disturbingly familiar. The paladin's family was lost to war—all of them—and he was the last, left to suffer a lonely and wretched life until he'd met his own horrible end. The Doctor had imagined the line between his own thoughts and the paladin's would be clearly delineated, yet they seem to sit beside one another with aching understanding. It makes it far more difficult than he'd anticipated, then, to resist what the spirit demands of him, to seek comfort by enacting vengeance on the opposing forces.
Unfortunately (or fortunately, perhaps), before the Doctor can act on the first impulse, he's stopped by Vanessa. Only temporarily, though. He's in control enough for the moment not to harm her when she gets in his way, but manages to elude her by binding her hands with the rope he'd kept hold of from the labyrinth. There was a flash of the Doctor in his eyes when he apologized to her, but then the spirit quickly took over again, insisting that she better not think of trying to follow him, before gagging her with a spare bowtie in his pocket. That done, he seeks out a few weapons to arm himself, the urge to fight now far too loud to quell. He would also not stop at harming anyone else who gets in his way. ]
closed to vanessa ives
The moment he agrees, the Other that settles into his mind feels disturbingly familiar. The paladin's family was lost to war—all of them—and he was the last, left to suffer a lonely and wretched life until he'd met his own horrible end. The Doctor had imagined the line between his own thoughts and the paladin's would be clearly delineated, yet they seem to sit beside one another with aching understanding. It makes it far more difficult than he'd anticipated, then, to resist what the spirit demands of him, to seek comfort by enacting vengeance on the opposing forces.
Unfortunately (or fortunately, perhaps), before the Doctor can act on the first impulse, he's stopped by Vanessa. Only temporarily, though. He's in control enough for the moment not to harm her when she gets in his way, but manages to elude her by binding her hands with the rope he'd kept hold of from the labyrinth. There was a flash of the Doctor in his eyes when he apologized to her, but then the spirit quickly took over again, insisting that she better not think of trying to follow him, before gagging her with a spare bowtie in his pocket. That done, he seeks out a few weapons to arm himself, the urge to fight now far too loud to quell. He would also not stop at harming anyone else who gets in his way. ]