"I know why you did what you did, but I still don't like it!" The Ninth Doctor proclaimed to the Tenth Doctor outragedly.

"I already know how you feel about Genocide, but they were just like the Daleks, Unreasonable Killing Machines, but if it makes you feel better, a handful escaped me into the woods!" The Tenth Doctor had defended his actions scatterbrainedly.

The Rose Tyler Twins are getting used to the Time Lord Regeneration of the Tenth Doctor while the Ninth Doctor worried about the chance that the Tenth Doctor was going insane and turning into the Valeyard that the Master warned him about during the Trial on the Planet Gallifrey.

The River Song Twins had never heard of the Valeyard in their own reality when the Ninth Doctor asked their advice, but they agreed to help the Tenth Doctor avoid turning down the wrong path regardless.

The Tenth Doctor had gone to his TARDIS to calm himself down and think about how to avoid debating all his past actions with the Ninth Doctor, starting with leaving UNIT Headquarters because the Werewolf Genocide had him thinking maybe he was wrong to turn his back on the Human Military after what he had to do on the Bad Wolf Planet.

Sure the Human Military had to train their people to avoid shooting anything they ran into on sight, but wandering around recklessly was only going to get his Rose Tyler killed if he keeps it up and the Tenth Doctor would not stand for that outcome at all!

The Tenth Doctor had tried to look up history files on the United Nations Intelligence Taskforce and found the history was the same until the Third Doctor vanished form the Planet Earth and the TARDIS was never seen again.

"No Fourth Doctor... no one to become the Valeyard in the future at all!" The Tenth Doctor says in realization.