One evening last week, I stopped in the little rural town of Presteigne, in Powys, just on dusk... and one of those timeshifts occurred.
It's a phenomenon best evoked on TV, when the picture goes into black and white and you see men in ankle-length macs and women with pins through their hats, and the men raise their trilbies to the women and offer them a Capstan Full Strength.
Presteigne at dusk
Well, OK, I may have exaggerated the odd period detail, but you get the idea: Presteigne at nightfall, especially when you haven't been there for a while, is part of another era.
For a start, there are no superstores. There's a traditional greengrocer's which, like my dad's old village shop, also sells fresh fish. There are shops trading in second hand goods overflowing on to the pavement. There's a flower shop and a town hall with a clock. And never many people about.
And not much light.
Which is the point. Presteigne is not merely old-fashioned. Because of Powys County Council's bid to reduce its electricity bill, it's also extremely dim.
No surprise, therefore, that this is the home of Ian Marchant, author of Something Of The Night, a new book about the strangeness of Britain after dark.
The title comes from Ann Widdecombe's memorable description of her Tory colleague, Michael Howard. Something of the night about him, Ann remarked - and we might have guessed that she was about to become a novelist.
Anyway, I've met both Michael Howard and Ian Marchant just the once, and maybe I'm not sufficiently attuned to this kind of aura but neither of them struck me as having much of the night about him. Michael Howard was fairly chatty and Ian Marchant seemed kind of sunny. And that's how his book begins.
Ian is one of those guys almost destined to live in Radnorshire, where incomers are rarely entirely normal. He's been a singer with various bands, including the almost-legendary Your Dad, and also a travel writer.
"I am a creature of the night," he writes. "Ninety per cent of this book has been written after dark."
His journey into the shadowlife is told in a series of flashbacks from an all-night drinking and confessional session with his mate Neil, a disabled small-time dope-dealer exiled to Ireland. To the strains of old pop music, most of which only one of them likes, we observe their wry but intermittently harrowing game of psychological strip-poker as the night makes its way towards the Hour of the Wolf.
Although it's scattered with statistics about sleep, dreams and circadian rhythms don't expect some kind of encyclopaedia of the nocturnal world. This is an increasingly personalised account, which begins with fireworks in Abergavenny, floodlit football, dog-racing and where to get the best pillows.
It moves on to the search for a nightingale in the Cotswolds and a visit to the Spacewatch observatory set up (in Radnorshire, obviously) to save the world from asteroid damage. There are memories of Ian's student years in Lampeter and a drive to Llanddewi Brefi where "the stars came crashing out in all their glory."
And then it does get dark.
The first danger signs appear in an account of a long drive from Cumbria home to Presteigne, listening to the car radio airing newly-discovered tapes of the poet Philip Larkin reading his own works. Larkin is a recurring murmur in this book which, sooner or later, had to tackle Aubade, arguably the most depressing poem ever written about lying awake with the knowledge that you're riding on a one-way ticket.
A weird, apparently-prophetic dream signals the sudden death of Ian's estranged first wife, turning him overnight into a single-parent suffering repeated panic attacks and the conviction that he won't see another morning. Then comes the temazepam, the Valium, the beta-blockers.
Meanwhile, we learn the tragic truth about how Neil came to be in Northern Ireland. And then there's the death of Ian's father, with whom he had a very negative relationship. And you remember a line from Chapter One.
"Night is when we are most likely to die, commit suicide... the time of our greatest fears."
It's not looking good. You examine the back fly-leaf to see if it says anything about this manuscript being found among the effects of the late Ian Marchant.
But, no, he was still around for the candlelit launch party in Presteigne. And you remember the night in a curiously bright and vibrant churchyard when - OK, with his system not exactly substance-free - he became aware "that I wasn't alone in the universe. that I was part of this beauty, somehow, and it was appropriate that I was there, and loved..."
It wasn't in Presteigne, but you can't have everything.