The Night of the Triffids

At the end of The Day of the Triffids, the hero, Bill Masen, his wife, and four-year-old son leave the British mainland to join a new colony on the Isle of Wight. The Night of the Triffids  takes up the story 25 years later. David Masen, the now grown-up son of Bill, is a pilot, still searching for a method of destroying the implacable triffid plant as it continues its worldwide march, seemingly intent on wiping out humankind. David eventually manages to reach New York, where a very different sort of colony has been set up, a colony whose members seem to be immune to the triffid string and where David comes face to face with an old enemy from his father's past.