On my way to the rendezvous I check my gear. I've got running shoes, spare batteries, compass, GPS, maps, network access, spyglass, notebook, tube card, gloves. I'm pumped full of caffeine, not sure what's coming, but ready to go for a burn.
When it starts it's almost an anticlimax. I wanted a mysterious stranger in a fedora; I got Father Christmas with a fake beard. But the instructions in the envelope are intriging: "Ten other pairs are playing. They all started in London. You have until 5pm to find them."
Apart from the promise of a Â£500 donation to Hope And Homes For Children if we succeed, that's all the information we have.
It's a brilliantly simple game (or psych experiment, in fact - we're being filmed), and gives us a free hand. So, of course, we're instantly all over our phones, trying to end this thing before we even have to move. We call the charity and leave a message, which pays off much later. We call friends. We call gaming contacts. We change our Facebook status. We try to pump the cameraman for information ("Got any mates working today? Where are they?")
This game hits the Strategy Point instantly.
It all comes together very fast. We find our first pair at the London Eye, agree a strategy and rendezvous point with them, and split up again. We take Leicester Square while they head for Trafalgar Square, printing fliers that say "Playing? London Eye 3pm" because we can't stay everywhere at once. By mid-afternoon we have everyone and we're at the pub.
Some people are surprised, but I'm not. If anything, I'm surprised that it took that long. The organiser reports that he's never had a team fail.
I found the dynamics fascinating. Perhaps it was rigged - perhaps the people who respond to this kind of ad are all the same - but we all thought the same way. Several pairs independently developed the same strategies, and at some point during the day, everyone went to Trafalgar Square. We all got along, even with multiple type-As each willing, but not insisting, on command. When the message got divided between 'London Eye 3pm' and 'Trafalgar Square 3pm', one of the players (an Iron Man) started a shuttle run taking in both.
Unfortunately, this is the kind of game you can only play once.
You can play a kind of virtual version in the comments, if you like - before you read any of the comments, work out your answer to this question:
"Players all over the world have received the instruction 'meet asap'. Assuming freedom of movement, where are you going to go? How will you find people when you get there?"
Then post your answer, and see if you found anyone.