Baby-Sitters' Island Adventure

Dawn and Claudia have a perfect day planned. They've invited Dawn's brother and three other kids to join them on a sailing race out to Greenpoint Island. The girls have even packed a picnic lunch for the adventure.
But then a big storm blows up in the middle of the race. And Claudia and Dawn and the kids never return from the island.
The Baby-sitters can't believe it's true--two of their members are missing!