The message arrived by email.
Lots of emails, to be accurate.
Lots of emails and lots of links ...
But I already knew the answer would be a resounding 'YES'.
I've always wanted to be a part of a flashmob ...
So what's it going to be? Pillow fight? Spontaneous disco dancing? Moon walking?
Neither - it's co-ordinated mobile phone alarms.
It's about putting pressure on governments to take a firm stand on climate change.
And it's organised by the Good Guys of Cyberspace, Avaaz.
Monday 21st September
Mel and I arrive at Parliament Square and head for our designated spot in front of Westminster Abbey.
I nudge Mel in the ribs.
'There!' I hiss. 'That's them!'
I indicate 3 women in blue t-shirts holding umbrellas and exchange conspiratorial nods with them.
'There - they're wearing blue and they're carrying umbrellas.'
Mel looks a trifle panicky. She hadn't read all the emails and has no idea what I'm talking about.
'So it's a signal. They know what's happening. Keep an eye on them.'
We do, trying to blend in and look like tourists. It's not easy and we both wish we had proper cameras instead of our mobiles. Our eyes dart round looking for other likely suspects. I smoke a fag. Mel eats a banana.
Oozing faux nonchalance, we head across the road and into the centre of the square.
Alarms ring out from 300 phones and assorted alarm clocks. From all over the square, 300 right arms are raised into the air.
There should be 302. Mel and I had synochronised with the website yet somehow we've managed to set our clocks 2 mins slow.
Never mind. We raise our silent phones in solidarity and hope no one will notice when they belatedly beep a couple of minutes later.
After joining in with the obligatory whoops and yells, we all turn north to face Mandela's statue.
'Tick, tick, tick,' we all chant, representing the time we have to save the planet ticking away.
Then we all call Gordon Brown on the numbers supplied in those emails.
It's all over and we drift away to get the bus home.
Due to road works and traffic jams, we were out for about 3 hours to take part in a 5 minute protest.
Was it worth it?
Well, apart from giving me the opportunity to spend some quality time with Mel on a glorious Autumn day, it seems the message did get through.
And it wasn't just us. All over the world events - over 2,200 of them - were taking place as ordinary people came together in a common cause to save our planet.
And I fulfilled a long held ambition to be part of a flashmob.
I'd post photos - if someone could just tell me how to get them from phone to blog ...
Other, less technically challenged people, fared better - see here.
Someone got me - can you see me?
You can still be part of the movement, even if you missed the day's events.
All you have to do is call the leader of your government, urging her or him to travel to Copenhagen for the climate talks in December and sign a fair, ambitious, and binding climate treaty.
You can find the appropriate phone numbers as well as photos and a live blog here.