Derek questioned Perry about the use of a terminator for a mission. Perry revealed that Skynet hit Eagle Rock Bunker with a bio-weapon that killed everyone, except for one person out of 200. They needed her back at Serrano Point. The General wanted to send a terminator in there because of their immunity to disease. Derek disagreed because of the chance one could go bad and kill who they're trying to save. Perry told Derek that once exposed to the disease, it's not known how long he has to survive. Derek was then sent on the mission.
Derek went to the Eagle Rock Bunker and was wearing a gas mask. He saw the dead bodies of countless people. He came across a woman, pregnant, lying down in bed with her two children beside her - all dead. Derek rushed out of the bunker, unable to comprehend what he saw. He pulled out his pistol and contemplates killing himself. He heard someone say "Excuse me" and drew his gun. It was Jesse Flores, another Resistance member.
Jesse and Derek met for the first time. She was trying to find the person who sent out an S.O.S. They headed into the bunker to find the girl who survived the bio-weapon attack. They went to a room in the back and knock on a door. The door opened to show Sydney Fields, the one who was immune to Skynet's bio-weapon. She told Jesse and Derek that their gas masks wouldn't help; that they're already infected. Derek told them to wait until it's night and then they'll head back to Serrano Point. Jesse was beginning to show symptoms of the disease. Sydney told them "It starts with a dry mouth. And then the sweats. And the fever and shaking starts. And then your lungs fill up with fluid and then you die. You don't have much time. It's coming."
Derek and Sydney helped Jesse back to Serrano Point.
Both Derek and Jesse were placed in medical beds, hooked up to IV's. Two people in sanitation suits come in with needles and inject something into their IV's (probably the antibody produced from Sydney Fields). The person tending to Derek is Lauren Fields, Sydney's older half-sister, who says "Thank you for saving my sister."
As a result of the success of this mission, the Resistance was able to develop a defense against Skynet's bioweapon.