Surveying many of Plato's dialogues from the early, middle, and late periods, prominent philosopher John M. Rist shows how Plato gradually came to realize the need for metaphysics to support his ethical position and that a rigorous ethics required a secure metaphysics grounded in universal values.

Plato came to realise that his earlier attempts to construct the relevant metaphysics, culminating in the Republic, were incomplete and his argumentation was insufficiently rigorous. Rist explains Plato's ongoing refinement of the theory of Forms and his hesitant attempts to relate claims about Forms to ideas about a divine mind (or god), which could offer an account of a transcendent reality as not only a formal and final cause of cosmic goodness and providence, but also an efficient cause.

Rist concludes the book by considering what more would be needed to complete Plato's theory without making damaging compromises to the basic principles of his metaphysics of morals. He sketches how Plato might reply to various contemporary approaches to moral reasoning and especially moral obligation.