Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Initial Situation
The narrator is sent to her "third posting," a position as Handmaid to the powerful Commander.
This is pretty straightforward: the narrator arrives at a new location while explaining both her position in society and how she got to it. It's kind of like the first "exposition" scene in a show like Law and Order, where the characters toss out a lot of backstory with straightforward dialogue.
Conflict
The Commander wants to be more than just Commander and Handmaid; that is, he wants to play Scrabble and take the narrator to a brothel called Jezebel's.
The whole point of the narrator's role in the Commander's house is as a sexless vessel to be impregnated. He's not supposed to enjoy being with her, and she's not supposed to threaten his relationship with his wife.
So when the Commander wants to enjoy some one-on-one time, he's getting his rocks off and putting the narrator in jeopardy. The fact that he wants to play Scrabble at first is way less predictable than his eventual desire to go to Jezebel's.
Complication
The Commander's Wife wants a baby so she tells the narrator to start sleeping with the chauffeur, Nick.
Clearly, breaking one rule isn't enough. Now the narrator has to get involved with another man, Nick, while keeping that part of her life from the Commander. It seems like she has a different private arrangement going on with everyone she knows. If that's not complicated, what is? This is a disaster waiting to happen.
Climax
The narrator starts to fall in love with Nick and thinks she might be pregnant. Meanwhile, she and her friend Ofglen have to go watch a Salvaging (execution). There, both women behave slightly abnormally and, as a result, put themselves in jeopardy.
Just as the narrator may be starting to carry a new life, she has to go observe death. While pregnancy should be a ticket to safety, the fact that she wants to be with Nick is only going to get the narrator into more trouble. As if on cue, she has to go to a Salvaging and see the terrible punishments that happen when women break the rules. This is reinforced when she sees Ofglen stand up for another person in the resistance. She begins to worry about how so little in her world is what it seems.
Suspense
The narrator finds out that Ofglen has compromised herself and vanished. The Commander's Wife finds out about the narrator's secret meetings with the Commander, and the narrator is forced to wait for some unknown punishment.
In what we like to call an "uh-oh" moment, Ofglen stops coming to their rendezvous. Another woman is there saying she's Ofglen. The narrator just saw the other Ofglen that morning—what's happened while she's been having lunch?
This stage in the book is full of different kinds of waiting. First the narrator has to wait to find out what happened to the real Ofglen (she killed herself) and whether this new one is also in the resistance (doesn't seem like it).
While she's trying to figure out whether she's in danger as a result of what the old Ofglen knew about her, the Commander's Wife confronts her about secretly spending time with the Commander. Now the narrator also has to wait to find out what revenge the Commander's Wife is going to take on her—which could be really, really bad. Only bad stuff seems to lie down this path.
Denouement
Men dressed as Eyes come to arrest the narrator. We don't know if they're really Eyes taking her away to be punished/killed or if they're resistance fighters there to rescue her.
This "unwinding" of events is remarkably ambiguous and suspenseful. The narrator says she doesn't know whether this event represents the end of her story or a new beginning. We never find out. In a neat inversion of the "Initial Situation" stage, the narrator is removed from her house and sent to a different posting of some kind, the likes of which we, and she, can only imagine.
Conclusion
At an academic conference several hundred years in the future, a professor provides historical context for the narrator's story and tries to explain what it all means.
For the scholars who speak in this section, the ideas here continue to be ambiguous. We can gather from the fact that the scholars are having the conference and discussing the Republic of Gilead as a thing of the past that at least the society that put the narrator through all that stuff is over. The chairperson of the conference is a woman, so obviously women can write, think, and participate in the world again.
The effects of the terrible Gileadean society are now studied from a safe historical distance, the way we might study the French Revolution. Yet these scholars, looking through their historic lenses, can't tell us what happened to the narrator, whether she made it, or even who she was. They can only guess that she managed to get out long enough to pass her story down to us.