For 10 points--name this expressionist one-act drama by August Strindberg.
It ends with a monologue in which the Student announces that appearances can mask evil, along with a warning to the audience that they cannot escape their sins.  Characters inlcude Hummel, a vampire; the Colonel, his enemy; a Mummy, the Colonel's wife, and an unnamed girl who lives on hyacinths.  For 10 points--name this expressionist one-act drama by August Strindberg.
It ends with a monologue in which the Student announces that appearances can mask evil, along with a warning to the audience that they cannot escape their sins.  
The Ghost Sonata or Spoksonaten