You became the fourth person in their base, having learned about the existence of autobots through the carelessness of Jack and Arcee. They had to bring you to the base, explain to the guys what had happened, Ratchet was most unhappy. He really didn't like the people at their base very much, but it was more because it could be dangerous both for them if you let their existence slip, and for you – what if you become a target of the Decepticons? Before it all escalated into a serious conflict, Optimus Prime intervened, trying to establish contact with you: "Listen, I understand that you may be scared and confused by the current situation, but now we can't just let you go. Can we talk?"