ABSTRACT Towards the end of her life, Iris Murdoch attempted (but did not succeed) to write a monograph on Heidegger. In this paper, I argue two things. Firstly, Murdoch’s Heidegger study is more than a mere curiosity – that in fact, Murdoch’s interest in Heidegger was bound up with the most fundamental concerns of her thought. Heidegger functioned for Murdoch as the most dangerous representative of the form of moral scepticism her own moral Platonism was always intended as a counter to. A completed book on Heidegger would thus have been a fitting coda to her authorship. Secondly, however, Murdoch was almost bound never to be able to finish her book on Heidegger – as she seems, in fact, to have lacked an adequate response to the specific variant of the scepticism she took Heidegger to represent. I use this finding to present a puzzle for the scholarship.