Lawyer Liam Foxwell starts at a performance appraisal. On his way home, he agonizes over replays of it on an embedded device called a "grain" that allows him to replay and rewatch memories in his eyes.
Arriving at a dinner party, he finds his wife Fi laughing with Jonas, and old friend of hers. Another guest, Hallam, talks at dinner about how she's been "grainless" for a year after the grain was "gouged" — removed from the skin behind her ear, likely so her memories could be sold.
Liam invites Jonas back to his and Fi's house, later claiming that he did this because Fi really wanted Jonas to come back with them. Fi invites the babysitter Gina, who was looking after their daughter Jody, to sleep upstairs for the night. Liam asks Fi about Jonas, and she identifies him as a brief relationship from Marrakesh that she previously mentioned. She says that they dated for a month, but Liam shows a memory of when Fi said that she and "Mr. Marrakesh" dated for only a week. The discussion becomes heated. They reconcile, after which Liam goes downstairs and drinks while agonizing over re-does of Fi and Jonas' interactions at the dinner party.
When Gina awakens the next morning, a drunk Liam asks her for opinions on his memories from the dinner party. Embarrassed, Fi gets Gina to leave, and Liam continues interrogating Fi. She now admits that her relationship with Jonas lasted for six months.
Liam drives to Jonas' house drunk, and Jonas is unhappy to see him. Liam taunts him, drinking further and eventually hitting Jonas. Hallam, who spent the night at Jonas', calls the police.
Liam wakes in his car, which crashed into a tree, and replays his memories. He assaulted Jonas by smashing a bottle, threatening him with the shards until he deleted his memories of Fi. At the dinner party the night before, Jonas admitted to rewatching hot times in earlier relationships, and Liam wants to stop him from doing this with memories of Fi.
While Jonas deletes the memories, Liam spots a memory of Jonas looking at Fi in bed at their now home. He goes back and asks Fi about it, who denies the story at each step until it's revealed that she slept with Jonas unprotected over a few days when Liam left over an argument. It was around the time that their child, Jody, was conceived.
Turning violent, Liam demands that she replays her memory, and she does.
Later, in an empty house, Liam reminisces on good memories around the house with Fi. He uses a razor blade and tweezers to bloodily remove his own grain in the bathroom mirror.
Liam's human insecurities are able to fester and grow out of control because he has a grain that allows him to replay every memory. Instead of forgetting about small details, he's able to obsess over the wording of the evaluators at his appraisal, and the facial expressions that Fi makes towards him.
Liam is abusive, but this stems from an extreme underlying insecurity. Charlie Booker, the creator of Black Mirror, called Liam "a weak, frightened, flawed person". The grain just enabled Liam's pre-existing insecurity and jealousy.
It hurts their relationship, too: small things that the couple would normally move past are weaponized and used in arguments. Liam pulls up a distant memory of Fi telling him a relationship was just a week, and Fi pulls up the memory of Liam inviting Jonas back to their house to prove that it was his idea.
Memory is imperfect, but when an implanted grain makes it perfect, people have trouble moving past anything and end up obsessing over the smallest details.
Not having an implanted grain is uncommon, and someone at the dinner party even describes "going grainless" as being "huge with hookers". Having the grain is essential for riding taxies, and boarding a plane even requires running through the last days of memories in front of security. Performance reviews for companies are supplemented by reviewing the past quarter of memories.
These obviously feel like huge breaches of privacy to us, but once you have this technology, not using it feels like a loss. How are you able to trust someone if they're not willing to show you what they've done recently, despite all those memories being at their fingertips?
Liam goes looking for the truth, but in the end he cannot handle it. Once he goes to extreme lengths to force Fi to show the memory of her cheating with Jonas, Liam goes back and watches the good memories with Fi. Then he gouges out his grain, and the screen goes black — implying that he lost his vision by gouging out the grain.
In the end, Liam chose imperfect memories over the perfect ones that the grain afforded him. He chose memories that fade and are imperfect over the pain of absolute truth and being unable to forget anything.
This page is referenced in: Black Mirror