Who is the narrator, can she or he read minds, and, more importantly, can we trust her or him?
Third Person (Omniscient)
The narrator of Thérèse Raquin can slip into the minds of all his characters, from Thérèse to Laurent to Mme Raquin. How cool is that? Very. But it's not unique, of course.
This story is told from the perspective of an omniscient, or all-knowing, third-person narrator.
And we think it makes perfect sense for Zola to write the novel in this way. Why? Because a third-person omniscient narrator is supposed to be unbiased—or, at least, equally biased toward each person's perspective. And so this narrative perspective closely mirrors the scientific objectivity that Zola wanted his novel to embody.
Of course, many readers find it difficult not to find truckloads of moralizing messages in the novel. The narrator does not explicitly condemn Thérèse or Laurent for committing murder, but the lengthy descriptions of their torturous descent into madness—and their final act of double suicide—inevitably implies that they are overcome by guilt. And so they must be punished for their crimes.
The bottom line is: whether or not the narrator of Thérèse Raquin can be accurately described as scientifically objective is open to debate. Let the games begin.