The story plays out over a course of a year between 1969 and 1970 with each chapter covering a month. Major historic moments play out in the background including the Moon Landing, Woodstock, X-Men comics, Lord of the Rings, the Vietnam War, the draft lottery, the Kent State shootings, the Beatles break-up, and one particular televised Nixon speech. During this time, Terry takes the place of her roommate, Stacey, to join a voluntary experiment at her university campus (the university is set at Bloomington and while it's not explicitly stated, I've assumed it's IU Bloomington) after Stacey gets a bad vibe from it. After a couple of months, the experiment shifts to Hawkins Lab.
During the experiments, Terry becomes friends with her fellow testees, Alice, Gloria, and Ken. Each of them are given doses of LSD and each go through different tests to see how their minds develop. Terry eventually begins to develop, after one particular experiment in a sensory-deprivation tank, a similar ability as Jane by traveling into a black void with shallow water. However, Terry's experience is more limited to communicating with one particular individual...Kali aka Eight.
Kali is five years old and Brenner brought her with him after recently taking over the lab because its previous personnel weren't gaining much results. Terry initially met Kali after becoming suspicious of Brenner's activities and tried to sneak into his office in order to learn what he was up to, but instead she first discovered Kali's room in a different part of the lab. The two develop a close bond over the course of the book, one that Terry is too trusting with Kali to hold secrets away from Brenner.
The other surprising development is how Alice, through electroshock treatment combined with the LSD (let's just ignore the pseudo science here...), begins seeing visions of monsters, including the Demogorgan, and even the Upside Down itself. And she then starts seeing the future, specifically when Jane breaks free Hawkins Lab. She doesn't initially understand what she's seeing, but when she recreates the experiment under the guidance of Terry, Gloria, and Ken, Gloria susses out that she's seeing the future because Alice describes personal computers and because she doesn't recognize any of the cars she sees (which she would've because she's a brilliant mechanic). Gloria is able to pick up on these nuances partially because of obsession with X-Men comics (where Jean Grey is her hero) as well as reading articles about technological development.
I don't recall how much information was revealed in the series about Jane's father, Andrew, but we see him for about half of the novel until Brenner pulls some strings behind the scenes by getting Andrew kicked out of college for protesting the war (which stood out when his two cohorts only get the slap on the wrist), which in turn makes him eligible for the draft. Brenner makes sure Andrew's lottery number is moved to the top of the list and he's quickly drafted and deployed. Terry doesn't discover that she's pregnant until about the same time he's killed in combat. We don't learn the details of his death, but during a Brenner POV, he notes even he was surprised by how quickly Andrew died (thus removing any speculation whether he further made sure Andrew was out of the picture).
The book ends a bit abruptly. After a pseudo-successful mission to convince Brenner to leave them alone and then plan later on to rescue Kali, Terry goes into premature labor (secretly induced by Brenner) and Brenner kidnaps Jane from a semi-conscious Terry. The doctors pretend she lost the child during the process, which leads to her sister, Becky, believing Terry has become delusion when she insists Brenner stole Jane (despite Terry telling Becky much of the shady dealings of Hawkins Lab prior going into labor). After giving birth, Terry discovers she can no longer visit the black void (which was able to do on her own without the aid of LSD as recently as the morning of giving birth), surmising that her abilities were always with Jane.
The epilogue closes with Terry planning to break into the Lab sometime in the future with Gloria and Ken's help to rescue Kali and Jane. I guess that means we'll be getting a sequel at some point because things haven't quite reached to how we saw Terry in seasons 1 and 2.
With that in mind, I'm planning to rewatch the episodes with her (as well as Kali's episode) to see how well things line up between this book and the series itself.