Okay, chapter seven is a weird one for plot summary. Why? Because there is no plot. Not a scrap, iota, or pinch of it. We're talking Michael Bay's Transformers level of plotlessness.
Just joking. It's not that bad. It's actually an investigator's notes on the androgynous gender and sexuality of the Gethenians.
So, we'll point out the key info for you, but don't expect any heart-pounding cliffhangers.
The Investigator believes that the Gethenians were experiments. He theorizes that they're humans made androgynous and then set loose millennia ago by the Hainish.
So, think human mice in a big old planet-shaped cage. Minus running wheels.
He can't understand why they picked such a planet. His best guess is that the planet used to be much nicer (less Arctic wasteland and more "California Love"). Then the Hainish civilization went belly-up and the poor Gethenians were left behind to suffer the planet's ice age.
The Gethenian sexual cycle goes for 26 to 28 days, so roughly a moon cycle. Also, you know, roughly the length of a woman's menstrual cycle, not that that could possibly mean anything. Or something.
During days 1 to 21, the Gethenians are in somer; i.e., they are androgynous and could care less.
By day 23, they enter kemmer and get to prowling for some action. When they find a partner, their hormones wake up, giving female genitalia to one partner and male to the other. Basically, all systems go.
The male/female change only lasts for one kemmer cycle, so "the mother of several children may be the father of several more" (7.4).
If you really like the dude you've mated with, you can vow kemmering, which is their version of marriage.
Odd though it may seem to us, incest is permitted with restrictions. Siblings aren't allowed to vow kemmering and can't continue to pair with each other after having one child together.
The investigator also notes how kemmer runs their entire civilization. Since anyone can be a mother, that means a mother can be anyone, from a guard to a baker to a politician. Anarchy! Downfall of civilization! Moral turpitude! You know, that sort of thing.
Anyway, what this means is that sexual discrimination is not only uncool, it's downright impossible.
Of course, this makes trying to live with the Gethenians very difficult for cisgendered human beings.