Who captures Anderton at the start of Part III? What is their conversation about?

Are you referring to when John is getting new eyes? John goes to a sketchy doctor to get his irises replaced so that he will not be identifiable in the system. The doctor sticks him with a needle unexpectedly and John holds him down on a table asking what it is. The doctor insists that it was anesthesia, saying, "You wouldn't break the hand of a violinist before a concert, please relax!" The doctor tells John he'll have to completely remove his eyes and replace them. John wants to keep his old eyes, even if they will be replaced, and the doctor agrees.