'You'll start with a blank map, that doesn't do more than show roughly what's water and what isn't'When the Walker family's holiday plans are ruined by Daddy having to work, the whole summer seems lost at sea. But a dull holiday for the children is too miserable to bear so their parents hatch a plan. The Swallows are to be marooned on an island with only a blank map and a little sailing dinghy. Their task? To explore and chart the area, avoid the endless mud and survive. And what do they discove