He follows that logic to some genuinely creepy places in the movie's final section. For much of the film, we follow Owen's character as he engages in a careful cat-and-mouse game with an unnamed hacker played by Seyfried. She's his only real suspect: A femme fatale type who provides memory-erasing services for rich clients looking to cover up illicit activity like art forgery or extramarital affairs. But after her services are rendered, many of her customers end up dead.
As Owen gets closer and closer to finding out the true identity of the murderer, his own eyes malfunction and the story takes on a hallucinatory quality. Throughout the movie, the viewer learns how the augmented-reality technology works through frequent point-of-view shots of small, low-stakes interactions like paying for food at a cafe or walking by a stranger on the street. Job titles, ages, and biographical details are displayed for every passerby, along with the occasional advertisement. (Niccol describes writing all this extra material to be "kinda a nightmare.") The biotech is advanced and the information is abundant, but not much more intrusive than having a few dozen tabs open in a web browser. When things go wrong, Owen's character is haunted by visions of rats, flames, and horrifying memories of his son's tragic death, which he's been trying to suppress.
"It was all playing on his own fears," says Niccol. "He's also confronted with the most painful time in his life. He's always going back to the memory of his son, and then the memory is hacked out of his record. What he's forced to watch is the moment where he took his eye off his son and his son was killed. To have that playing over and over again is a very special kind of torture."
Is Seyfried the one pulling the strings on his mind's eye? Nope. In the movie's final showdown, we learn she wasn't the one behind the murders. Instead, it was all the work of Cyrus Frear, a security expert assigned to the case and played with sinister flair by Halt and Catch Fire's Mark O'Brien. The details are better left to unpack for yourself as you watch, because there are some genuinely confusing techno-mysteries to solve, but suffice to say Seyfried's character has kept herself anonymous by implanting bits of her life into her clients' records, and Frear is part of a network of hackers keeping Seyfried's character safe.
"She's found the most ingenious way to hide, which was to actually put a fragment of her life in your life record, in my life record, and in the life records of billions of people," says Niccol when asked about Cyrus's revelation. "You'd need an algorithm to stitch it all back together, which I found very interesting. That you can actually hide in plain site like that, so if you were replaying your life you'd get maybe one frame of hers. But it would be very hard for you to find it. It's a bit of a mind-fuck."