The Day of the Triffids - John Wyndham
No matter how many other great SF books I read, this one will always make it into my top 5. I'd guess that most people have a vague idea of the plot - giant walking plants with poisonous stings terrorise a humanity blinded by terrible green lights from space - but this book is far superior to the B-movie schlock you'd expect. Wyndham's elegant and often amusing tale focuses much less on the monsters and much more on the humans; the story mostly concerns the sociological outcomes of the disaster, and the ways in which the survivors try to rebuild their world.
The story is told from the first-person perspective of Bill Masen, a biochemist from a triffid farm who has escaped the mass blinding of humanity by a lucky accident. Waking up in a hospital bed after an eye injury, he finds a world suddenly devastated by its loss of sight, and a city full of desperate people now incapable of looking after themselves. With fellow survivor Josella, he joins up with the few remaining sighted people to start building a new society; amid all the human chaos, no-one heeds his warnings about the triffids, until they start to become a real danger. Covering a period of several years after the disaster, we get a much more complete picture of the post-apocalyptic world than just a few chapters of monster-hunting.
Above it all rose the Houses of Parliament, with the hands of the clock stopped at three minutes past six. It was difficult to believe that all that meant nothing any more, that now it was just a pretentious confection in uncertain stone which could decay in peace. Let it shower its crumbling pinnacles on to the terrace as it would - there would be no more indignant members complaining of the risk to their valuable lives. Into those halls which had in their day set world echoes to good intentions and sad expediencies, the roofs would in due course fall; there would be none to stop them, and none to care. Alongside, the Thames flowed imperturbably on. So it would flow until the day the Embankments crumbled and the water spread out and Westminster became once more an island in a marsh.
Given the setting of mid-20th-century London, the horror is genteel and understated, with atmosphere taking precedence over action. Bill Masen is a down-to-earth and unsensational narrator, still able to see the ridiculous side of things and drily self-deprecate his own fears and heroics, and this adds a very believable note to what might otherwise be a hard-to-swallow situation. Unlike many other Mutant Monster! fictions from the same era (Triffids was published in 1951), the triffids themselves are by no means the cause of the disaster, but are instead merely a previously indispensible agricultural hybrid, now taking opportunistic advantage of humanity's discomfiture.
The story's Cold War origins are still apparent in the background - there are plenty of hints that the burgeoning military satellite-count is a cause of unease, and while the triffids are not a dastardly Communist plot (except perhaps an economic one), their genetic origins are shrouded in Iron Curtain secrecy. However, this is not really a tale of international conspiracy; it's a story about luck and survival by some plucky and pragmatic Brits, and with its optimism and dry humour it remains one of the most pleasant, readable and above all believable post-apocalyptic novels out there.