With their usual meeting place being cleaned out and painted, the Secret Seven have to find somewhere else to meet. So it's voted on that they use a cave in the quarry near the field where Peter's father grows the potatoes. But it's soon clear to the Seven that someone else is using the cave, when food, cushions and books go missing. Then clever Scamper finds a note book on the cave floor, belonging to Albert Tanner and inside are the words – Meet him on post-office seat 8.30pm, 15th, Ted! Now the Seven have a lovely juicy mystery to solve!