Two different groups of children encounter one another on a small piece of land in a lake which they both live by. Both groups try to claim the land as theirs, role-playing as two sets of enemy pirates. While this happens they encounter another boat and a stranger, they must now work together to work out who he is and why he is there, but have they got themselves involved in something much bigger?
Four children (the Swallows) on holiday in the Lake District sail on their own to an island and start a war with rival children (the Amazons). In the meantime, a mysterious man on a houseboat accuses them of a crime they did not commit.