We were just sitting down to dinner when we heard the roar coming up the street.
We ran to the window and saw a group of hooded kids smashing up the mobile phone shop across from us.
Within minutes, they'd torn most of the facade off and the whole street was full of young people on a rampage.
There had been a few police around earlier in the evening, as there had been rumours on Twitter of Clapham Junction being targeted.
The Waitrose supermarket and a few other shops had closed early and put their shutters down. When it kicked off, though, there wasn't a police officer in sight.
We watched out our front window as pandemonium reigned for more than three hours.
Our street, St John's Road, is busy at the best of times, with a lot of foot traffic between Clapham Junction station and the bars and restaurants nearby.
It's quite short and narrow, but there are a lot of mobile phone and electronics shops along it.
It was these that the looters went for most ferociously, and with obvious intent.
They were clearly organised. They knew where the cops were and some were shouting out directions to each other. Currys, an electronics shop, and Carphone Warehouse were stripped clean.
Kids were walking around with big flat-screen TVs, laptops, colour printers and arm fulls of clothes.
One rode around casually on a stolen Boris bike (named after London mayor Boris Johnson) with a TV and a box of trainers balanced on the handle bars. When there was nothing more to loot, they took the fire extinguishers.
One guy eventually got bored and smashed it into the window of the Natwest bank. They left Waterstones, a book store, untouched.
The looters compared their plunder, casting aside the less desirable items that they'd picked up just because they were there. Menacing and frightening as this was to watch, they didn't seem angry.
They were out of control, sure, but they were excited. It was almost festive; they thought this was hilarious.
Luckily, the few brave rubberneckers and residents unlucky enough to be caught on their way home were ignored as the mob concentrated on ransacking the shops.
Finally a few police vans arrived, an hour-and-a-half after the first wave of violence started, and the looters took off back down the street.
The riot police quickly tried to secure Currys but it was much too late.
The police moved down the street, grabbing a few looters and arresting them, but then ended up in a standoff outside chef Jamie Oliver's Recipease shop.
The police pinned a couple of rioters to the ground but started coming under fire.
Looters up a side-street were hurling rocks and bricks. Then they charged with their police vans and cleared the street.
Eventually, the police secured the street and restored a tenuous calm.
This morning (last night NZ time) we woke to find St Johns Road cordoned off, with debris strewn everywhere: glass, bits of smashed electronics, empty shoe boxes.
Shellshocked residents and shopkeepers milled around, surveying the staggering damage and wondering what the hell had just happened.
* Alex Spence is a New Zealand journalist who has lived in London for seven years.