Bill Masen is lying in his hospital bed as he recovers from an accident with a triffid, a poisonous and carnivorous plant, that has left him temporarily blind. What he doesn't realise is that, overnight, the world has changed.

It slowly dawns on Bill that something truly terrible has happened overnight. Leaving the hospital, he meets and forms a bond with Jo Payton. Jo also missed the comet's display and so, like Bill, has not suffered the blindness visited upon others.

Bill and Jo sight a signal from the University Tower where a group of survivors have formed, and they both face a difficult moral decision about helping others. Bill becomes increasingly concerned about the triffids attacking.

Now separated from Jo, Bill is held captive by Coker and forced to do his bidding, leading the blind and foraging for food. If he is ever to find Jo again he will have to escape.

As the people are dying, the triffids seem to be multiplying in number. Bill returns to the University looking for Jo and runs into Coker again before heading south.

Bill and Jo have settled into life at the farmhouse, becoming self-sufficient and fending off triffid attacks with flame-throwers. But their quiet peace is soon to be shattered.