Mystery on the Fourteenth Floor — Dorothy Martin

Twelve-year-old Vickie felt like she had lost everything when her family moved to the city. Her old friends were too far away for her to see them every day, and she was terribly lonely. The whole summer was going to be like this -- just blah.

But that was before she heard the news report of the kidnapping and before the SOS sign appeared in a window of the next building. Was the kidnap victim being held there?