Like in the show, Joe meets Beck, a writer in grad school, when she comes into the bookstore where he works in New York City. As she checks out with her purchases, they make playful banter and she pays with a credit card. To Joe, this means she deliberately wants him to know her full name — Guinevere Beck — because otherwise she would've paid with cash. Of course, since the story is told entirely from Joe's perspective, there's a lot more language of him graphically describing and objectifying Beck's appearance (specifically her lack of a bra).
By searching her name online, he's able to find all of her public social media profiles, which leads him to discover who all of her friends are and even where she lives. He spends days standing on the stoop opposite her ground-floor apartment in the West Village watching her every move, going so far as to buy disguises from a thrift store so neighbours don't realise the same guy is standing there day after day. Eventually he gets into her apartment by calling a false gas leak into the city and posing as her boyfriend, and he's able to find out a bunch more about her by searching through her laptop.
After reading a few of her emails, he finds out she's reading a new story she's written at a bar in Brooklyn and shows up there. He doesn't approach her but later follows her out to the subway (she's alone and very drunk), where she slips and falls onto the tracks. He saves her and they share a cab back to her place, but she gets out alone to meet her on-again, off-again hookup, Benji. What she doesn't realise is that Joe slipped her phone into his pocket in the cab and now has access to her every move.
By tracking her likes, dislikes, and whereabouts, Joe is able to slowly but surely manipulate Beck into a romantic relationship with him. She's never fully on board, always cutting things off just as they start to get serious, which only serves to further fuel Joe's obsession with making her his.
Image Source: Lifetime