In 1910, the two sisters, eleven- and twelve-year-old Maud and Addie,
are eagerly anticipating their Summer Social in Mahone Bay, Nova Scotia.
However, the event does not quite go according to plan, and the two
girls are swept out to sea as they are rowing home at the day's end.
They find themselves adrift in the unforgiving North Atlantic with only
the contents of a picnic hamper to sustain them and a carriage blanket
to keep them warm. Finding their way through stormy seas, the girls
finally make landfall on a deserted island. With string and a jackknife
recovered from Maud's pockets and a parasol and novel contributed by
Addie, the girls create a world for themselves among the island dunes,
keeping company with sea birds and other sea creatures. Their ensuing
adventures test their wits and, in the process, forge a bond that
enables them to survive.