Mandie and the Tornado — Lois Gladys Leppard

Mandie sniffs out a mystery brewing even before leaving school for the spring holidays. Uncle John's letter said someone--no one knew who--was living in the old, dilapidated house on the edge of the Shaw property. When Mandie arrives home, she discovers that her only clue is a faint, flickering light sporadically shining from the ramshackle building. Late-night investigations make Mandie and her friends certain that someone is indeed hiding out, but who can it be? Why all the secrecy?