This tale is told in Iain McGilchrist's book The Master and his Emissary. The introduction of the book is found here.
According to him the Master is our right hemisphere and the Emissary our left one.
The book is not an oversimplified popularization of the functions of hemispheres but largely based on extensive neurologic and neuropsychologic research, especially among split brain and brain lesion patients. McGilchrist projects his interesting, thorough analysis of the main differences and similarities of our hemispheres onto the canvas of poetry, music, human body language, in fact onto the whole evolutional and cultural history.
The modern Western culture reflects the unbalanced overpower of the left hemisphere's narrow, theoretically based, self-consisted model of the world, which is tremendously powerful in mastering the physical world, but which does not understand the infinite world outside of all theories.
Typical for the right hemisphere is the ability to grasp intutively what is going on, but it needs the left hemisphere to express it. It knows that it needs the left one, but the left one does not know that it does not know, thus believing to be self-sufficient, needing no one else, eventually collapsing the whole kingdom in ruins.
McGilchrist's allegory is remarkably suitable to demonstrate the most important task for dream groups: by reviving the right hemisphere, helping the Master return to the throne from exile, restoring the equilibrium between both hemispheres; finding ways where both knowledge and understanding, analysis and intuition, science and art can work in unison, recognizing their deep dependence of each other, and their importance of their united teamwork for mental health of human beings for the well-being of the whole community and culture.
Dream groups have in this task a tremendous advantage: they have in their hands the most powerful tool for exploration of the most unfathomable abysses of our psyche: the product of (predominantly) the right hemisphere; our dreams, illuminating the innocent, most authentic depths of the human soul. If we are wise, understanding what we have seen with the help of dreams, allowing them to speak with their own voice, our emissary may understand better its proper place, serving the Master, spreading around the wisdom of our innermost being, helping the kingdom of humanity to prosper in human relations.