There are too many entertainment films these days (as, really, there were in the past) but the situation would be better if more of them resembled the 1968 thriller, Pretty Poison.  It offers the subject of mental illness without boring or confusing us, and is uncomfortably convincing about violence and characterization.  Lorenzo Semple Jr. was perspicacious in writing the book-derived script, and Noel Black directed tastefully and unpretentiously.

As a mentally disturbed young man, Tony Perkins does not provide the distinction he did as the mentally disturbed dude in Psycho.  As his peculiar girlfriend, Tuesday Weld is intriguing and subtle.  A chemistry exists between both.  The chemistry that makes up the Weld character is quite pretty.  I was pleased to have found Pretty Poison on YouTube.