Order and chaos
The imagery of the first act is centered around the removal of a wall which is classic imagery for order and chaos. The wall is an imposed established instrument of separation, and the plot to remove it is a symbol for change and time. Because the imagery takes place in a political sphere, the chaotic progress of time has proletariat undertones, because the rigid authority of Sir Philip's reign has become imbalanced. This makes Peter a force for change, like a catalyst.
Theater and production
The overtly literal imagery of Peter's political activism leads him into an inverse imagery where he has to pretend to fit in. He is still a chaotic character, but he is having to fit in with people without tipping them off to his being a fugitive. His performance of "expected behavior" makes the theater imagery a suitable depiction of his emotional landscape. This relationship between his emotional thought life and the manifestation of imagery around him is also the dynamic of Kit's journey of androgyny.
Pursuit of the fugitive
The novel is a "cat and mouse" story where the big, bad guy is in constant pursuit of the hero, looming around every corner. The imagery is a full-blown depiction of paranoia, because Peter is not like James Bond or something. He is scared of being caught and beheaded, which he heard through the grapevine is what Sir Philip wants to do to him. This is the imagery that is shown in the Yellow Gentlemen's constant meddling and in the eventual victory of the people—the wall is felled.
The romantic twist
Now, this is the genius of good story-telling. The imageries described above are the sections of a broader imagery that contains the whole story in a subtle way. When Kit and Peter reveal to the audience that they are falling in love, the story is revealed to be a "falling in love" story instead of the story it seemed to be at the time. This is a way of comment on true love by imagery. The emergence of romance in Peter's story was completely unpredictable and in some ways, absurd. He didn't know he was in the story of how he met his spouse until suddenly, it was happening.
