Set in the Cold War era, The Day of the Triffids imagines the rise of a new species which cirumstances place in conflict with people. The triffids are valuable human-engineered plants; they are cultivated in virtually every country on earth. They possess some remarkable characteristics: they are mobile, they seem to be intelligent, they can communicate with each other and they eat flesh. Triffids lash out with a toxic sting which immediately immobilises and quickly kills their prey. The triffids then wait for the flesh to decompose before using their 'muscular' sting to prise free a nutritious meal. In the tropics, they are a real threat to human life. However, in the developed world where they are cultivated for their valuable oil, humanity appears to have them under control...

On a May morning in London, Bill Masen wakes in a hospital bed to uncertainty. The clocks are stiking eight but no-one has come to remove the bandages from his eyes. He is a triffid researcher, and has accidentally had his eyes splashed with triffid venom. He discovers that, thanks to his bandages, he is one of a very few people who have retained their sight following a beautiful but blinding meteor shower the night before.  In one disastrous moment, the human-triffid balance of power has been overturned.

In the anarchic streets of blind London, Bill encounters Josella Playton, who is also still able to see. At the University of London, a handful of people under the leadership of Michael Beadley are organising a coordinated response to this disaster. The response is radical: a new world, so Beadley's group argue, needs new rules; they propose to rebuild the sighted human population by breeding sighted men with more than one partner. However before this programme gets underway, a radical named Coker raids the university and captures both Bill and Josella.

They are each harnessed to a blind guard and told to take care of small groups of blind people. Coker wants them to keep people alive and together until help comes from the 'Yanks'. He has not realised that the disaster is global: no help is coming.

Bill's band come under attack from escaped triffids and a rogue human group led by a violent man named Torrence.  His charges begin to fall ill from some mysterious deadly ailment, and eventually he is left alone. He goes in search of Josella. At the university, he discovers that the Beadley group have moved to Tynsham Manor in Wiltshire. He joins forces with Coker, and they set off together with lorries full of provisions.

At Tynsham Manor they find a religious group under the leadership of Ms Durrant; they have broken with Beadley's group on the grounds that Beadley's propositions for the future are immoral. After searching further afield for Beadley, Bill remembers Josella's earlier mention of a farmhouse in West Sussex. This is Shirning Farm, where he eventually finds Josella and her blind friends. Bill and Josella settle down to farm the land and establish a self-sufficient life together at Shirning, with a young girl they have adopted called Susan. Over the ensuing years, they come under increasing threat from the triffids, which are drawn to human settlements.

In the end they are found by one of Beadley's scouts in a helicopter. The Shirning Farm group are invited to move to the relative safety of the Isle of Wight, where a more civilised life awaits, and where Bill can use his research knowledge to seek a long-term solution to the challenge of the triffids. They are reluctant to leave Shirning, until the arrival of the violent Torrence and his scavenger followers.

This group has settled on a feudal solution to the world's problems; they propose that Bill and Josella establish a kind of feudal seigneury at Shirning, while Susan is relocated. Bill and Josella play along with the despotic idea and hold a party to welcome the men. Alcohol flows freely. In the dead of night, the Shirning residents slip away to the Isle of Wight. Behind them, triffids make their way into the farm grounds...