The Girl Who Couldn't Remember — Carolyn Keene

MIND GAMES IN MINOSHA...

Nancy, Bess, and George are determined to get away from it all so they decide to spend a week at a secluded cabin on Wisconsin's Lake Minosha. But where Nancy goes, trouble is sure to follow. A knock comes at her door, a girl slumps unconscious into her arms, and Nancy's back in business!

The girl says her name is Toby, but that's all she knows -- her memory has gone blank. As Nancy pieces together the puzzle of Toby's past, she discovers that the mystery girl is at the center of a burning controversy about the future of the beautiful lakefront. The local sheriff claims that Toby has stolen some important documents -- but when Nancy receives a warning to stay off the case, she vows to unlock Toby's secret before the sheriff locks Toby away.