It's blackberry picking time, and the Fabulous Four are in for an adventure. Sarah is not well and is in bed, but Sam, Rosie and John go out to pick blackberries. They hope to find lots of the juicy fruit so that they can sell them and build up the fund for a tricycle for a friend of theirs. But when they get to the common, they see that all of the bushes have already been picked.
Then they discover a better place to go blackberrying - the neighbour's garden! And to their astonishment, they find an amazing hidey hole. What do they find inside it? And who has been using it as a secret place?