My psycho-analytic work has convinced me that when in the baby's mind the conflicts between love and hate arise, and the fears of losing the loved one become active, a very important step is made in development.

Allegedly two of the first children Melanie Klein analyzed were her son and daughter. A compromise was eventually reached whereby three distinct training groups were formed within the British Psycho-Analytic Society with Anna Freud's influence remaining largely predominant in the US. Set in London in 1934 the play involves a conflict between Melanie Klein and her daughter Melitta Schmideberg after the death of Melanie's son Hans Klein.

She was a leading innovator in theorizing object relations theory.