He listens intently to River as she explains her friend, this Doctor must be a far greater man than he is. He listens to her explain about the world this Time Lord came from, and as a being from another dimension he's yet to hear of this race until now. "Time travel is not unique among Time Lords, before I fell, I was capable of time travel. It was very draining, but I could do it.

But, perhaps your friend if he would be able to can help us." Castiel thinks, perhaps time travel can be the key to their problems. If he can just go back in time to warn himself of what would happen if he sided with Metatron. "My friends are trying to help, but we're facing an army, so all the help we can get would be wonderful."