<P> This episode was filmed sixth in the series' production run . </P> <P> The Number Two from the prior episode "The Chimes of Big Ben" (Leo McKern) returns to the Village . He calls his superiors and obtains permission to undertake a dangerous technique called "Degree Absolute" in a final attempt to break Number Six and learn why he resigned from his position as an intelligence agent . Number Six is put into a trance state, causing his mind to regress back to his childhood . He is taken to the "Embryo Room", deep below the Green Dome, filled with various props, as well as a caged room that contains living space and a kitchen . He, Number Two, and the Butler (Angelo Muscat) are subsequently locked into the room via a timer that will unlock the room after one week . </P> <P> Number Two begins to use regressive therapy following Shakespeare's Seven Ages of Man, using the various props to enact a series of psychodramas, with Number Two playing the authority figure (e.g., father, headmaster, employer) and Number Six the subject (child, student, employee). Each drama is aimed at trying to make Number Six explain why he resigned . During the first six of these, Number Two finds Number Six has developed an aversion to saying the word "six". Number Two also comes to like and respect Number Six as he learns more about him . </P> <P> On the final day, Number Two enacts the role of military jailer, harshly interrogating Number Six as a prisoner of war . Number Two's efforts seem to have effect as Number Two starts to blather on reasons for resigning, but he becomes concerned when Number Six says he knew too much, including about Number Two . Number Two becomes agitated, and Number Six continues to call him a fool and an idiot . Suddenly, Number Six starts counting down from "six", and by the time he's reached zero, has regained full control of his mind . Already exhausted from his efforts, Number Two is shocked and collapses . He explains to Number Six that Degree Absolute, a well - known psychiatric technique, has its risks to the one performing the therapy if they have their own psychological problems . Number Six shows his understanding in a brief role reversal (by asking Number Two "Why don't you resign?"), much to Number Two's delighted amusement . </P>

Once upon a time who is the prisoner