What could possibly go wrong . . .?
Anne has gathered Julian, Dick, George and, of course, Timmy, together for a last nostalgic jaunt in the countryside together before grown-up responsibilities take the four cousins off in different directions. It's only natural that they find their way onto Kirrin Island for a look around, as this might be the last time they're here together as a group.
They are planning just to spend the night there and come home the next day, perhaps with a little exploring in the dungeon for old time's sake. But that night they hear the country has gone into lockdown. They are not allowed to leave.
With their usual resourcefulness, they are determined to make the best of it, and remain cheerful and healthy. As Anne keeps saying: They're lucky, really, to have all this countryside and fresh air at their disposal!