The Kidnapping is in the series titled The Cedar Tree Mysteries.  It comes after the book, The Secret of Cedar Tree Mansion. 

The Kidnapping features the same characters in the previous books:  Christy, Megan, Penny, Ron, Abby, and Randy.  In this book, Christy is kidnapped in the middle of the night.  Megan saw what happened, but after she tried to follow them, she ran out of gas.  While she is out of her car, she is hit on the head and can't remember what happened to her or why she was in the middle of the road at night.