Peter and Brian are planning to leave the family to go play laser tag with Joe and Quagmire. Lois objects, saying Peter agreed to spend Sundays with his family, but Peter and Brian leave anyway. Peter wins at laser tag and comes home to a disgusted Lois. Brian defends Peter but Lois claims that Brian is just taking his side because they hang out and would never have met if it was not for circumstance. Despite further objections, Brian and Peter head out with Joe and Quagmire to go drinking at the Drunken Clam. While on the way, they see strange lights in the sky and run into them. At this point they blackout before waking up in a hospital and realising Quahog is empty and they have no memory of who they are. Finding that they are the only four people in the town, they team up and walk on, wondering who they are. They chance upon Peter's car, which is crashed by the side of the road. They find out Peter was driving and also find out Peter's address. They head to Spooner Street, where Brian realises they live there. However, they make wrong assumptions, such as that Brian is Quagmire's dog and Joe is a stripper. While in Peter's house the other three see a fake newspaper front page that he bought after winning the laser tag and begin to suspect he is an alien who has killed the rest of the city. Joe and Quagmire head off to get guns while Brian spies on Peter. Peter and Brian then begin to bond, so by the time Joe and Quagmire return, Brian goes back inside the house to warn Peter. They attempt to escape but Joe and Quagmire head them off. Just as Joe is about to shoot, Brian jumps in the way, sacrificing himself to save Peter's life. Then Brian wakes up, startled and confused. It turns out Stewie had chosen to capture and hook them up to a computer system simulating the world to see if Brian and Peter were just friends through circumstance, but the simulation has proved they do belong together. Brian then looks upon a tank where Stewie has also hooked up Lois, Meg and Bonnie to an identical system, only to see them fighting instead of investigating their circumstances.