In this quiet, slow and ultimately powerful production, directed by Gordon Edelstein and featuring strong performances from Jim Dale and Carla Gugino, Ms. Harris plays Miss Helen, an elderly South African woman who has hitherto seemed gracious, fretful and rather prosaic. Now she has given undiluted voice to the kind of fear that lurks in everyone — one of those personal fears that are so profound that people shirk from naming them. She is magnificent and shrunken, harrowed and harrowing.