Speckled Band Classics A

A yong woman, Helen Stoner, lives alone with stepfather in a big, old house. Two years ago her sister died suddenly one night after screaming in a terrified voive:
The speckled band !
The sister appeared to have died of fright. Nowe Helen hears strange sounds in the night. She is very frightened. Is she going to die like her sister?
She comes to Sherlock Holmes for help.