I got hold of this; then, instinctively, instead of returning as I had come, went to the window. It was confusedly present to me that I ought to place myself where he had stood. I did so; I applied my face to the pane and looked, as he had looked, into the room. As if, at this moment, to show me exactly what his range had been, Mrs. Grose, as I had done for himself just before, came in from the hall. With this I had the full image of a repetition of what had already occurred. She saw me as I had seen my own visitant; she pulled up short as I had done; I gave her something of the shock that I had received. She turned white, and this made me ask myself if I had blanched as much. She stared, in short, and retreated on just my lines, and I knew she had then passed out and come round to me and that I should presently meet her. I remained where I was, and while I waited I thought of more things than one. But there's only one I take space to mention. I wondered why she should be scared. (4.6)
This role reversal is really fascinating – the replacement of Quint with the Governess is the first thing that makes us wonder what her deal really is. The line "I wondered why she should be scared" implies that perhaps the Governess has horrifying qualities of her own that she's not yet aware of.
"Another person – this time; but a figure of quite as unmistakable horror and evil: a woman in black, pale and dreadful – with such an air also, and such a face! – on the other side of the lake. I was there with the child – quiet for the hour; and in the midst of it she came." (7.3)
Miss Jessel apparently just exudes "evil" – we're not sure how or why the Governess feels this way, though. This is just part of our narrator's desire to pin things down as either good or evil, even when they don't comfortably fit in these categories.
The apparition had reached the landing halfway up and was therefore on the spot nearest the window, where at sight of me, it stopped short and fixed me exactly as it had fixed me from the tower and from the garden. He knew me as well as I knew him; and so, in the cold, faint twilight, with a glimmer in the high glass and another on the polish of the oak stair below, we faced each other in our common intensity. He was absolutely, on this occasion, a living, detestable, dangerous presence. But that was not the wonder of wonders; I reserve this distinction for quite another circumstance: the circumstance that dread had unmistakably quitted me and that there was nothing in me there that didn't meet and measure him. (9.5)
In this struggle between good and evil (or at least, between two parties vaguely representing the latter), the Governess and Quint are equally matched – and this equality adds to the rather ambiguous nature of the Governess's character.
I drew a great security in this particular from her mere smooth aspect. There was nothing in her fresh face to pass on to others my horrible confidences. She believed me, I was sure, absolutely: if she hadn't I don't know what would have become of me, for I couldn't have borne the business alone. But she was a magnificent monument to the blessing of a want of imagination, and if she could see in our little charges nothing but their beauty and amiability, their happiness and cleverness, she had no direct communication with the sources of my trouble. If they had been at all visibly blighted or battered, she would doubtless have grown, on tracing it back, haggard enough to match them; as matters stood, however, I could feel her, when she surveyed them, with her large white arms folded and the habit of serenity in all her look, thank the Lord's mercy that if they were ruined the pieces would still serve. (11.1)
The only character that is undoubtedly "good" in this story is Mrs. Grose – we never once question her innate goodness or loyalty, though all the other characters are potentially either good or evil – or both.
"They're not mine – they're not ours. They're his and they're hers!"
"Quint's and that woman's?"
"Quint's and that woman's. They want to get to them."
Oh, how, at this, poor Mrs. Grose appeared to study them! "But for what?"
"For the love of all the evil that, in those dreadful days, the pair put into them. And to ply them with that evil still, to keep up the work of demons, is what brings the others back." (12.2-3)
Interestingly, though the idea of evil is omnipresent in the story, it's never given an explanation – as far as we know, Quint and Jessel are really just evil for evil's sake.
Tormented, in the hall, with difficulties and obstacles, I remember sinking down at the foot of the staircase – suddenly collapsing there on the lowest step and then, with a revulsion, recalling that it was exactly where more than a month before, in the darkness of night and just so bowed with evil things I had seen the specter of the most horrible of women. (15.4)
Again, the Governess's alignment with the ghosts – this time with Miss Jessel – makes us question whether she herself is good or evil, or if anyone can concretely be defined in such a manner.
"I've made up my mind. I came home, my dear," I went on, "for a talk with Miss Jessel."
I had by this time formed the habit of having Mrs. Grose literally well in hand in advance of my sounding that note: so that even now, as she bravely blinked under the signal of my word, I could keep her comparatively firm. "A talk! Do you mean she spoke?"
"It came to that. I found her, on my return, in the schoolroom."
"And what did she say?" I can hear the good woman still, and the candor of her stupefaction.
"That she suffers the torments – !"
It was this, of a truth, that made her, as she filled out my picture, gape. "Do you mean," she faltered," – of the lost?"
"Of the lost. Of the damned." (16.6-7)
Hmm…interesting. Who's being deceptive now, Governess? We don't know why the Governess decides to fabricate this little section of the story – after all, we saw her interaction with Miss Jessel in the schoolroom, and there was no conversation that we could see. However, here she tells Mrs. Grose that she's received confirmation that the ghost is damned. Can it be that the Governess is just trying to create her own justification for her actions by bringing religion into it?
The appearance was full upon us that I had already had to deal with here: Peter Quint had come into view like a sentinel before a prison. The next thing I saw was that, from outside, he had reached the window, and then I knew that, close to the glass and glaring in through it, he offered once more to the room his white face of damnation. It represents but grossly what took place within me at the sight to say that on the second my decision was made; yet I believe that no woman so overwhelmed ever in so short a time recovered her grasp of the act. It came to me in the very horror of the immediate presence that the act would be, seeing and facing what I saw and faced, to keep the boy himself unaware. The inspiration – I can call it by no other name – was that I felt how voluntarily, how transcendently, I might. It was like fighting with a demon for a human soul, and when I had fairly so appraised it I saw how the human soul – held out, in the tremor of my hands, at arm's length – had a perfect dew of sweat on a lovely childish forehead. (24.1)
The struggle between good and evil is made perfectly clear here – Quint and the Governess are actually fighting over Miles's soul.
[…] he was at me in a white rage, bewildered, glaring vainly over the place and missing wholly, though it now, to my sense, filled the room like the taste of poison, the wide, overwhelming presence. "It's he?"
I was so determined to have all my proof that I flashed into ice to challenge him. "Whom do you mean by 'he'?"
"Peter Quint – you devil!" His face gave again, round the room, its convulsed supplication. "Where?"
They are in my ears still, his supreme surrender of the name and his tribute to my devotion. "What does he matter now, my own? – what will he ever matter? I have you," I launched at the beast, "but he has lost you forever!" Then, for the demonstration of my work, "There, there!" I said to Miles. (24.22-25)
In the Governess's triumphant eyes, Quint has lost the battle for Miles – however, the boy's wording makes it unclear who is the "devil" here, the Governess or Quint.