Greta, in the studio synopsis, is described as an 'eccentric French piano player' and Isabelle Huppert playing her could have taught Baby Jane Bette Davis a few things in playing/being crazy.
This is a female dominated film with, more or less, cameos by Stephen Rhea as a private detective and an estranged dad played by Colm Feore. His daughter, Francis, played by Chloe Grace Moretz, rooms with Erica, played by Maika Monroe, her best friend who has a spacious brick apartment bought by her father in New York City. Francis finds Greta's purse on a subway and returns it to her and to say anything more would spoil the craziness, that makes no sense but is a lot of fun to watch and all will be forgotten by the time you leave the theatre. Well, not all, because watching Isabelle Huppert flipping a table, no spoiler as it is in the preview as is something she does with music that you will laugh at with guilt feelings, maybe!
Neil Jordon, a favorite director of mine since "The Crying Game", adds his very odd take on people of all kinds and he has willing accomplices with his actresses, especially, again, with Isabelle Huppert. His direction, and her acting, certainly aren't Oscar winners let alone contenders, but they are certainly entertaining.
There are many holes in the screenplay written by Jordon and Ray Wright and many scenes you will laugh at which I don't think was intended. Plus if you want violence and jump out of your seat surprises you may or may not find them here depending on your ability to suspend belief at the movies.
Did I like "Greta"? Do I recommend "Greta"? Yes and no--how's that for being definite? Or is it a 'red herring' you might find in the movie?