After unbandaging his eyes, he wanders through an anarchic London full of almost entirely sightless inhabitants, and witnesses civilization collapsing around him.
 Masen meets a sighted woman, wealthy novelist Josella Playton, who was being forcibly used as a guide by a violent blind man. She and Masen begin to fall in love and decide to leave London. Lured by a single light that they see shining in an otherwise darkened city, Bill and Josella discover a group of sighted survivors at a London university building. 
The group is led by a man named Beadley, who plans to establish a colony in the countryside. Beadley wishes to take only sighted men who will take several wives, sighted or otherwise, to rapidly rebuild the human population. Bill and Josella decide to join the group.
The polygamous principles of this scheme appal one of the other leaders of the group, the religious Miss Durrant. Before this schism can be dealt with a man called Wilfred Coker takes it upon himself to save as many of the blind as possible. He stages a mock fire at the university and during the ensuing chaos kidnaps a number of sighted individuals including Bill and Josella. Each is chained to a squad of blind people and forced to lead them around London, collecting rapidly diminishing food and other supplies. 

Bill and his squad find themselves beset by escaped triffids as well as by an aggressive rival gang of scavengers led by a ruthless, red-haired man.
Masen nevertheless sticks with his squad until its members all begin dying of some unknown disease. He leaves and attempts to find Josella, but his only lead is an address left behind by the now-departed members of Beadley's group. Thrown together with a repentant Coker, he drives to the place, a country estate named Tynsham in Wiltshire, but neither Beadley nor Josella is there; Durrant has taken charge and organised the community along "Christian" lines. Masen and Coker fruitlessly search for Beadley and Josella for several days, before Bill remembers a chance comment Josella made about a country home in Sussex. He sets off in search of it, while Coker returns to Tynsham.
Bill is joined by a young sighted girl named Susan; they succeed in locating Josella, who is indeed at the Sussex house. Bill and Josella consider themselves to be married, and see Susan as their daughter. They attempt to make the Sussex farm into a self-sufficient colony, with reasonable success. 

The triffids grow ever more numerous, crowding in and surrounding their small island of civilization. Years pass, during which it becomes steadily harder to keep out the encroaching plants - at least two triffid break-ins are recorded during the novel.
One day a helicopter pilot representative of Beadley's faction lands at the farm and reports that the group has established a successful colony on the Isle of Wight, and that Coker survived to join them. 
Despite their ongoing struggles, the Masens are reluctant to leave their home, but their hand is forced by the arrival the next day of a squad of soldiers who represent a despotic new government which is setting up feudal enclaves across the country. Masen recognizes the leader, Torrence, as the redheaded man from London. 
Torrence announces his intention to place many more blind survivors under the Masens' care and to move Susan to another enclave. After feigning general agreement, the Masens disable the soldiers' vehicle and flee during the night. They join the Isle of Wight colony, and settle down to the long struggle ahead, determined to find a way to destroy the triffids and reclaim Earth for humanity.