Hello! An interesting question. Critics remain convinced that Jack Maggs is a thinly veiled autobiography of Charles Dickens and also a re-write of Great Expectations.
Did you know that in Australia, the term magsman refers to a confidence trickster, an individual who relishes telling stories? The origin of the word is 19th century English; mag means to prattle. Significantly, the protagonist, Jack Maggs, is an Australian convict, who secretly returns to England, risking his own arrest on English soil. He is soon to unwittingly tell the story of his past to the unscrupulous Tobias Oates. Maggs seems to be the incarnation of the infamous Abel Magwitch from Great Expectations, also an Australian convict, who returns secretly to see Pip, the young orphan. Pip is stunned to find out that his secret benefactor is Abel Magwitch. In Jack Maggs, Maggs returns to London to find Henry Phipps, the young orphan he turned into a gentleman with the wealth he earned in New South Wales, Australia. The similarities end there. Henry Phipps is dissolute and self-absorbed; indeed, he bears no resemblance to the grateful Pip, who visits Magwitch in prison. Jack Maggs himself is far younger than Abel Magwitch.
In Jack Maggs, the protagonist goes in search for Henry Phipps, but ends up in the household of Percy Buckle as a footman. There, at a dinner party, he meets the famous author, Tobias Oates. This is significant because Oates eventually uses mesmerism to help Maggs deal with his tic douloureux (severe intermittent pain to one side of the face caused by irritation to the trigeminal nerve).
Maggs needs to find what he calls a "thief-taker," a man who can supposedly find any individual in England; Maggs thinks that is the only way to find Henry Phipps. Meanwhile, the irrepressible Tobias Oates thinks he now has a goldmine on his hands: through his hypnotic sessions with Maggs, he hopes to mine a bevy of secrets and personal stories from the unfortunate Maggs. Maggs is afraid that his convict past will be extracted from these powerful cerebral experiments. He tells Tobias that he would rather live with his pain than reveal his inner secrets, but Tobias disarms him by showing him the book where he writes everything that Maggs says when he is under the influence of Oates' mesmeric powers. Unbeknownst to Maggs, there are two sets of books. The first set of books is the decoy, if you will:
..and with all the various explanations Oates constructed, it never once occurred to Jack Maggs that these "transcriptions" had been fabricated by the writer to hide the true nature of his exploration. (pp 86)
The second set of books holds the real secrets of Maggs' mind, "a corner of a house by London Bridge, a trampled body in a penal colony." Yet, this second set of books leaves the reader wondering at the efficacy of Tobias Oates' notes:
For the writer was stumbling through the dark of the convict's past, groping in the shadows, describing what was often a mirror held up to his own turbulent and fearful soul.
Oates is not above misrepresenting the truth to Maggs; he tells the hapless convict that hobgoblins live in his head "like beetles in a fallen log," and that demons are responsible for his torturous pain. He tells Maggs that he alone can take away that suffering. At a session in Oates' home, Oates is triumphant. He tells his sister-in-law, Lizzie:
Don't you see what I now possess? A memory I can enter and leave. Leave, and then return to...What a treasure house, eh, Buckle?
It's the Criminal Mind...awaiting its first cartographer.
Tobias Oates means to use Maggs' stories to write a successful novel. In other words, Oates has no problems taking advantage of and profiting from the misery and past suffering of the convict. But are the disjointed memories belonging to a tortured soul like Maggs reliable?
So, what are the traits which go against Tobias Oates' talent as a writer?
I would say that Tobias Oates' greed for money and his penchant for unscrupulous transactions possibly renders him an unreliable narrator in his own work. He is not above coloring the truth for a chance at making a profit. How can we presumably trust the word of an author who is not above manipulating our emotions for his own aggrandizement? Works of fiction might withstand the assault on truth; indeed, the suspension of reality is one of the hallmarks of enjoyable fiction. But non-fiction? Not so much.
Tobias Oates' distrust of doctors and his inferiority complex regarding the medical profession also renders him unfit to be an objective voice in literature. He writes "how time and again, they (the doctors) betray his heroes, abandon them, act snobbishly and capriciously towards the poor." When invited to a dinner with surgeons at the Hippocratic Institute, his bias against doctors is evident; this bias not only renders him paralyzed at the thought of dining with the eminent surgeons, it effectively minimizes any possibility of neutrality in his portrayals of doctors in his writing.
As my post was quite long, here are some links you might enjoy to further aid you in your understanding of Jack Maggs.
The first link discusses a review of Jack Maggs.
You might also look into a book titled Witnessing The Past: History and Post Colonialism In Australian Historical Novels. I don't see the book on Amazon, but you might be able to borrow it through your library if you are interested. This book discusses the story of Jack Maggs by Peter Carey, himself an Australian author. The link below includes excerpts of analysis on the novel. Enjoy!
I hope this answers your query. Thanks for the question.