Baker's allegory of compromise
The novelist does something funny with Baker's character by showing his constant character dilemmas about "doing the right thing." But as it goes along, the reader can't help but feel that Baker is only looking for ways to get out of doing the right thing. His story ends up being an allegory for moral compromise, and it ends with his undeniable, indefensible abandonment of his new family. This betrayal is proof that Baker is morally compromised.
Australia as a metaphor
The colony of Australia represents something about Britain to the people who live there. First, it represents that Britain is kind of shady, because they pretty much only sent the worst criminals to the new colony. That means that Australia represents Britain's dark side, and the confusing logic of how Britain made their decisions regarding Australia ends up being the focal point of the Playmaker Farquhad's play.
The wife in Plymouth
To Baker, his wife becomes nothing more than a symbol, a symbol for his past vows. When he starts regretting his commitments, his wife morphs into a symbol for the burden of doing the right thing, instead of just indulging desires. By the time Baker heads back to England, he has completely betrayed her.
The play
The play represents the novel. What the play indicates to its audience is quite literally the same as what the reader reads from the book. The play is a subtle criticism of European colonialism and the confusing, sometimes cruel decisions of the British government. In other words, the novel exists to suggest that Britain might be wrong for its methods and decisions.
The new girlfriend
The most innocent, easily-cherished person in the new colony is Mary Brenham. There's only one small problem; she's a kleptomaniac with a track record for petty theft. This is symbolic, because it also represents her function in the story. She steals a petty object, the affection of Baker. She represents the violent tendencies of Australian colonizers.
