Gabrielle Zevin's Tomorrow, and Tomorrow, and Tomorrow follows two lifelong friends, Sadie and Sam, who, as game developers, use video games as a tool to understand life and cope with loss. Set against the backdrop of the dynamic 1990s and early 2000s, the book vividly captures the social and cultural landscape of pre- and post-millennial America while following the protagonists' personal development and struggles over the course of two decades.

Sadie and Sam meet as children in a hospital. There, Sadie is supporting her sister, Alice, through leukemia treatments and Sam is recovering from a car accident that took his mother's life and left him with a disabled leg. They quickly become friends, bonding over their shared love for video games. Unfortunately, they drift apart when Sam incorrectly assumes Sadie only spends time with him to fulfill the community service requirements for her Bat Mitzvah.

Years later, Sam studies math at Harvard, and Sadie studies computer science at MIT. They coincidentally run into each other at a train station, and Sam calls out to Sadie, who gives him Solution, a game she developed, and asks for his opinion. For the first time in years, the pair speak, rekindling their connection.

Sam loves the game and decides that he wants to make a game with Sadie. Working with Sam’s wealthy and charismatic roommate, Marx Watanabe, an actor turned game producer, the trio establishes a company called Unfair Games and, soon after, develops a highly successful game: Ichigo.

As the story progresses, Unfair Games gains fame and popularity. However, rampant sexism in the gaming industry results in Sam getting all the spotlight, while Sadie is relegated to the background, where she decides to concentrate on developing the sequel to Ichigo.

Sadie’s mentor and lover, Dov Mirzah, whose engine they used for Ichigo's graphics, is confident in her abilities but expresses that sexism remains rampant in the gaming industry, making no effort to hide the harsh realities she must overcome. Despite his warning, Sadie is determined to prove her value as a video game designer and, in doing so, pave the path for other women like her. 

The sequel to Ichigo falls short of its predecessor’s success and is criticized for its lack of creativity. The Unfair Games team relocates to California, and Sam, who had his leg amputated after falling and breaking his foot, expresses his desire to create a third Ichigo game.

However, Sadie disagrees, preferring to develop new and innovative games rather than chasing commercial success. The pair comes to a compromise and collaborate on a new game, Both Sides, which features two worlds: Mapletown, created by Sam, and Myre Landing, developed by Sadie.

Both Sides faces criticism upon release, but Mapletown—and its most iconic character, Mayor Maze—gain popularity. Pursuing the success of Mapletown, Unfair Games launches Mapleworld, an MMORPG that introduces inclusive features such as gender-neutral marriage to the beloved game. While this displeases some Mapleworld members, it delights many and lands Unfair Games an even larger fan base.

Despite facing regular hate for his perspective, Sam begins to use his game to express his political views. Playing under his gaming name, Mazer, he begins to gain popularity and, to some, notoriety. However, his personal success feels meaningless, as he experiences intense heartbreak when Marx and Sadie reveal they are a couple and, soon after, plan to purchase a house together.

During the promotions for Sadie's murder mystery theater game, Master of the Revels , Sam assists her as a producer, though he keeps his distance. Marx remains at the company office in Venice...