This tuneful thriller is loaded with mystery, action, and laughter.  Strange things are happening at spooky Saltmarsh Manor, the old house next to Greystone Academy, a boarding school for teenagers.  Aunt Martha and Aunt Helen have seen ghosts, heard the organ play with no one at the keys and been terrorized by everything from a hangman’s noose to clanking chains.  Madam Orloff, the psychic, says the spirit of August Grimm, also known as ’Mad Monk,’ has returned.  But what does he want?  Obviously, it’s a case for Christie Blake, the devoted fan of mystery writer, Agatha Christie.  Christie involves the student body of Greystone Academy in these strange happenings.  The chills and thrills end in a hair-raising seance that pits Christie against evil forces.  The show is designed for simple production and written for easy rehearsals.  The music score is a hit parade of lively tunes — the lovely ballad, ’Christie,’ the big show-stopper, ’And Then There Were None,’ the spooky tune, ’We’re Living In A Haunted House,’ and the old-time vaudeville-style number, ’Chips Off The Old Block,’ plus many more.  The characters are a joy to play, everything from bewildered parents, sinister visitors, and suspicious servants to a squad of bubbling and eager detectives.