The Twisted Window by Lois Duncan
The Twisted Window is geared toward advanced JR high/high school aged people. It was short, and the plot was interesting. Some of the ideas were a little juvenile for a young adult reader; nevertheless, I would recommend it to anyone who loves Goosebumps.
Tracy, a high school junior, becomes embroiled in the problems of a strange boy, who asks her assistance in "snatching" his half-sister from her father who has allegedly kidnapped her.