If you go down to the Tavistock Piazza in Portobello Market, keep an eye out for a mysterious sweet shop in a silver caravan that's taken up residence for the past week. Don't expect to be paying pennies for your sweets though - this shop trades only in knowledge, and only something no one else knows.
For the next two days, you can trade your secrets for sherberts, your tittle-tattle for toffee, knowledge nuggets for nougat, and help contribute to The Big Book of Everything We Know, compiled by the folks that overran the Barbican with Vampires last year.
Then, come the end of the month, the book will be closed, pondered upon and combined into a performance on the 30th at 7pm, and 5pm on Saturday 31st and Sunday 1st August. Your words, stories and secrets will form an integral part of the resulting production, so get down there this week to feed their minds and your belly.