Jane, Mark, Katharine, and Martha are spending the summer in the country, by a lake, when they catch a turtle who has the power to grant wishes (but prefers the wishes to be water-based). At first they wish for a magical lake, but that proves excessive and burdensome (no one wants water babies, pirates, and mermaids in the same square meter of water), so they get their wishes one-by-one. That doesn't work substantially better; the older girls wish themselves into teenagers one night, and then there's the unfortunate matter of the hostile tribe that wishes to burn them alive. Still, they survive, and when they find a pirate's treasure, they know exactly what to do with it.
This report prepared by Ivy