This is a story about complicated friendships and creative partnerships, the kind of deep intertwining of lives that an outsider might easy mistake for romantic or sexual but is in fact something closer to a platonic soulmate situation. It's semi-nonlinear, and covers much of the life of Sam Masur and Sadie Green from their meeting in a children's hospital in the late 1980s into their mid-30s and careers. Sam and Sadie become best friends through a chance meeting, and bonded over a shared love video games. A childhood grievance breaks their friendship, and they do not speak for many years until reconnecting in Massachusetts where Sadie is studying game design at MIT, and Sam mathematics at Harvard. Sam throws out a wild idea: in the summer break before their senior years, they should build a computer game together. So begins a tumultuous collaboration that absolutely delighted me, as did the epistolary elements, the mid-book shift into second person narration, and the stories within the story. What did not delight me was the abusive boyfriend who takes up a lot of space in the first 1/3 of the story. If student/teacher relationships and their accompanying unfair power dynamics, marital infidelity, or brief descriptions of physical abuse are a no-go, this book may not be for you. However, when this character mostly exited the narrative I began to enjoy it more and more and I can see why so many people added it to their favorite books of the year lists last year.