Murdoch and Nietzsche start from with the same assumptions when considering morality. But interestingly, they end up in different places.
Iris Murdoch, in the essay The Sovereignty of Good over other Concepts, gives her starting assumptions as follows (p. 76-7)
That human beings are naturally selfish seems true on the evidence, whenever and however we look at them, in spite of a very small number of apparent exceptions. […]
That human life has no external point or Telos is a view as difficult to argue as its opposite, and I shall simply assert it. I can see no evidence to suggest that human life is not something self-contained.
These principles are ones Nietzsche would agree with. Added to this the disagreement among those who consider the matter as to what principles morality is based on, lead Nietzsche to scepticism about the existence of morality (see the upcoming paper by Leiter which outlines Nietzsche’s position in full).
Murdoch takes another path. She agrees that modern attempts to analyse moral concepts without success, but argues that the failure is due to the abandonment of images and metaphors, which are “the fundamental forms of our awareness of our condition”. Though such philosophy does not arrive at a conclusion, it does contain concepts which lose substance when an attempt is made to remove the metaphorical aspects.