Plot summary

Ronan and Beatrix each receive a message from their father, Alex, who requests they meet him. Curious, they separately converge at their father's house, where they find him missing, though Ronan recovers a strange, ball-shaped device. When Harry, Beatrix's friend, arrives, he joins them in their attempts to locate their father despite Ronan's dislike for him. Harry, a public defender, suggests that they contact the police. However, Captain Stone can offer little help to them, as they have no evidence of wrongdoing. He directs them to the building Alex described and tells them that it is abandoned.[3] The three find the building empty and covered in graffiti that describes alternate time-lines and histories. Initially dismissive of the seemingly nonsensical graffiti, they discover that the building has transported them to an alternate Earth devastated by nuclear blasts. When they see a roving patrol shoot down pedestrians, they flee back into the building, where they meet Polly. Polly, a traveler between worlds, explains that the building transports anyone within it to a new, random world if they return to it in exactly 36 hours. In hostile worlds such as the one in which they currently reside, she suggests that they stay inside the building and not interact with the locals. The group sleeps to pass the time.