The Day of the Triffids - John Wyndham

When a freak cosmic event renders most of the Earth's population blind, Bill Masen - one of the lucky few to keep his sight - finds himself trapped in a London jammed with sightless mobs who prey on those who can still see. But another menace stalks blind and sighted alike. With nobody to stop them the Triffids - walking carnivorous plants with lethal stingers - rise up as humanity stumbles and falls.