15-year-old Neil Miller is orphaned following a car accident and goes to live with his grandparents in Winchelsea, England. Neil suffers post traumatic stress from the car accident and stays detached from his peers despite their occasional attempts to involve him. News travels of a new disease, called the CalcuttaPlague due to its origin, which accelerates the aging process in human beings. The plague appears to be uniformly fatal, and although initially only affects those of already advanced years, it quickly progresses until it takes the life of a 2-year-old girl who Neil finds and attempts to look after. During this time Neil notes that he has contracted the plague, but after a brief fever it leaves him unaffected. The death of the girl leaves Neil the sole survivor of Winchelsea, and after deciding that Winchelsea is becoming dangerous - due in part to packs of wild dogs - he leaves for London, taking first a manualMini which he has difficulty driving, followed by an automaticJaguar. Arriving in London he meets his first fellow survivor - the mentally unbalanced Clive, who although friendly towards Neil, during the night vandalizes his car to the point of destroying it, steals his mother's ring that Neil had kept which was the only memory of his mother he had visibly, and then abandons him in central London. After finding the body of another survivor, Peter, who had committed suicide only hours before Neil found him, he is again despondent, but finds evidence of other survivors which brings him into contact with Billie and Lucy. Billie is openly hostile towards Neil, and it is implied that she has suffered in some way either during the plague or directly after it, but Neil becomes friends with Lucy and starts a romantic relationship with her - much to Billie's disgust. During this time Neil notes that the dogs have been supplanted by even more dangerous rats, and at least one big cat has escaped from a local zoo and although unseen is heard outside their flat. To this end Neil arms himself with a pistol and ammunition taken from a sporting goods shop. Billie and Neil continue to argue over an unspecified period of time, with Lucy gradually taking Neil's side in arguments, until eventually during a foraging expedition Billie attempts to kill Neil by stabbing him in the back with a kitchen knife. The attack is shown to be premeditated as when Neil tries to defend himself with the gun he finds that it has been unloaded. Neil is injured, but overpowers Billie and returns to Lucy, where they lock Billie out and decide to move on to a previously discussed farmhouse. Billie arrives back at the house and pleads with both Lucy and Neil to let her back in, but they decide that they could never trust her again, and leave her outside. In the last paragraph of the book Neil abruptly changes his mind, feeling that he would never get over the guilt of leaving Billie to die, and with Lucy goes downstairs to open the door and let her back inside.
