Bandersnatch is an interactive film. A brief tutorial, specific to the device being streamed on, explains to the viewer how to make choices. When presented with a choice point, the user has ten seconds to make a choice or a default decision is made for them. The average viewing is 90 minutes, though the quickest path ends after 40 minutes. There are 150 minutes of unique footage divided into 250 segments, yielding over one trillion possible paths that the viewer can take. In some cases, the same scene is reachable in multiple ways but will present the viewer with different choices based on the way they reached it. In other cases, certain loops guide viewers to a specific narrative regardless of the choices they make.
Netflix reported that there are five "main" endings, with variants within each ending; some endings are intercut with credits, similar to other Black Mirror episodes. Producer Russell McLean said there are between ten and twelve endings, some of which are more concrete than others, and according to director David Slade, there are a few "golden eggs" endings that are difficult to achieve. No ending is considered "prescribed" over any other, according to series creator Charlie Brooker and executive producer Annabel Jones, particularly as they felt some endings were not truly endings in the traditional sense. In most cases, when the viewer reaches an ending, the interactive film gives the player the option to redo a last critical choice in order to explore different content, sometimes with a fast-forward through early parts of a storyline already seen. Some endings may become impossible to reach based on choices made by the viewer unless they opt to restart the film.
In Britain in July 1984, a young programmer named Stefan Butler is adapting a "choose your own adventure" book owned by his late mother, Bandersnatch by Jerome F. Davies, into a revolutionary adventure game. Stefan pitches it to the video game company Tuckersoft, which is run by Mohan Thakur and employs the famous game creator Colin Ritman. Stefan is given the choice of accepting or rejecting help from the company in developing the game. If Stefan accepts, Colin says he chose the "wrong path". The game is released months later and critically panned as "designed by committee". Stefan considers trying again, and the film returns to the day of the offer, and the viewer is given the same choice.
Rejecting the offer, Stefan begins to work on the game on his own from his bedroom, given a September deadline. As the game becomes more complex, Stefan's life is torn between his career and his role, and he eventually becomes stressed and hostile to his father, Peter. He visits Dr. R. Haynes's clinic for therapy. The viewer may have Stefan explain to Dr. Haynes about his mother's death: when he was five, Peter confiscated his stuffed rabbit toy. His mother was delayed by Stefan's refusal to leave without the rabbit and the train she took derailed, killing her. Stefan feels responsible for her death. Dr. Haynes prescribes Stefan medicine, which the viewer can choose to have Stefan take or flush down the toilet.
The viewer may have Stefan accept an invitation to Colin's flat, where he lives with his girlfriend Kitty and infant daughter Pearl. The viewer is offered to take LSD with Colin or not; however, in the latter case Colin then spikes Stefan's tea with the drug. Colin rants about secret government mind-control programs and alternate timelines. To demonstrate his theories, Colin demands Stefan choose one of them to jump off the balcony. If Stefan jumps, he dies and the game is finished by Tuckersoft to poor reviews. If Colin jumps, the whole encounter is revealed to be a dream, but Colin is absent in future scenes and remembers the event in that dream.
As the deadline to deliver the game looms, Stefan begins to feel he is being controlled by outside forces. Stefan finds his life mirroring that of Davies, about whom he learns through a book and a documentary that Colin gives him. Like Davies, he sees recurring imagery of a "branching pathway" symbol, which seemingly led to Davies beheading his own wife. As he begins to mentally break down, the viewer has multiple options to explain to Stefan who has been controlling him, including the option for Stefan to be told that he is being watched on Netflix in the 21st century. The viewer may discover a locked safe that contains either Stefan's old toy rabbit or documents about him being monitored as part of an experiment.
There are numerous possible endings. Stefan may choose to confront his therapist, after which it may be revealed that he is on a film set and that his "dad" is a fellow actor. One set of choices leads to Stefan seemingly crossing through a mirror to his five-year-old self, and then choosing whether to "die" with his mother in the train crash, causing him to suddenly die in the present. In other paths, the viewer has the option to make Stefan kill his father, and then bury or chop up the body. Burying it leads to Stefan being jailed before the release of the game. Dismembering it leads to the successful release of the game, but Stefan goes to prison shortly after, and the game is recalled and destroyed. Other scenes show Mohan, Colin, or Kitty arriving at Stefan's house, sometimes with the option to kill the characters. In some endings, the viewer is shown the critical reaction to the Bandersnatch game and the fate of Tuckersoft, which may go out of business. One ending (chop up the body) concludes in the present day with an adult Pearl, now a programmer for Netflix, attempting to adapt Bandersnatch into an interactive film. The viewer chooses for her to pour tea over her computer or destroy it, which implies she may go down the same path Davies and Stefan did.
