A bizarre new form of vegetation appears all across the world. Known as Triffids, they are plants able to 'walk', communicate with each other and feed off human corpses. In England, young Bill Masen becomes the first victim of a Triffid sting and, although it is usually fatal, he survives the attack and humans decimate the plants, later nurturing them in captivity for their lucrative vegetable oil.

In the near future, Masen - now a researcher in his thirties - is temporarily blinded by another Triffid sting and is thus unable to witness a spectacular meteor storm, which renders the vast majority of humans sightless. He teams up Jo, who also escaped the storm's effects, and the two become lovers, initially joining a ruthless, militaristic group of sighted humans.

Masen is kidnapped by the kindly but over-zealous Jack Coker and forced to work with his bands of blind and sighted survivors until this hopeful micro-society is virtually destroyed by a mysterious plague.

Along with Jo, their adopted daughter, young son, and three friends, they spend several relatively tranquil years in a remote, self-sufficient property. Meanwhile, England suffers physical decay, Triffids grow more numerous and powerful and hope for humanity begins to dwindle.

When the Triffids' increasing threat seems inexorable they again meet Coker, who tells them of an island commune dedicated to restoring democratic order and destroying the lethal plants. After avoiding the attentions of a fascistic, paramilitary organisation bent on world domination, they desert their home to join Coker and his quest for a new, decent society and the total eradication of Triffids.