When Joel finally gets her to the Fireflies, it is discovered that Ellie requires an operation to remove the mutant strain of the Cordyceps fungus growing on her brain, which may be used to create a vaccine; the operation will likely kill her. While she is being prepared for surgery, Joel kills Marlene and the Fireflies, makes his way to the operating room, and carries Ellie to safety.[1] Because she was unconscious during the battle, Ellie is unaware of what has transpired. As they leave the hospital, Joel lies about the events, telling her that the Fireflies had found many other subjects, and had stopped looking for a cure.[2] When Ellie later confronts him about it, describing her survivor's guilt and demanding to know the truth, Joel reassures her that he is telling the truth; she replies "Okay".[32]