A terrorist from where Brody was held hostage was captured by Americans and brought to the CIA. Carrie and Saul bring Brody in to help with the interrogation. He helps them out, but later asks if he can look at the man in the eye, to face his torturer.
Carrie doesn't allow it. The man finally talks, giving up an email address that leads them back to the professor they followed earlier in the season. Brody convinces Estes to let him see the terrorist, and they get into a bit of a fight. They later find that the man killed himself with a razor blade, and that the professor packed up and left his house. Carrie credits Brody with both of these happenings.