"But considering how he was all zappy when he arrived, and in a manic state, how could you blame me for locking him up? And even afterwards! You have to admit, your former regenerations have been pretty intense, if not downright dangerous, what to speak of sneaky! It wouldn't have been responsible of me to let him loose without making sure he wasn't going to be a danger to anybody. I thought I was being generous by letting him wander around the TARDIS!" The Doctor rolled his eyes. "The Master never had any other friends. Minions, yes. He enjoys being alone because his ego is the only company he'll tolerate." The Doctor wasn't being very nice, because he was still bitter.
Listening to Missy's explanation, the Doctor's mind became more peaceful, so that by the time she was finished, he was holding her hand again - it was a natural thing, done as a reflex, without forethought. He found Missy's method much more attractive than fighting against the thorns of the Master's ego. He made a frustrated sigh, finding it difficult to find the words to say, until he finally told her, "Thank you. I hope the Master in you doesn't take offense, but I find it much easier to speak with you."