The following version of this short story was used to create the guide: Doerr, Anthony. "The Master's Castle." The Best Short Stories 2021: The O. Henry Prize Winners. Vintage Anchor Publishing, 2021.

Anthony Doerr's short story "The Master's Castle" is written from the third-person point of view and in the present tense. The story is set in multiple locations and across several decades of time. The following summary employs the present tense and a linear mode of explanation.

When Basil Bebbington is in high school, he is not good at many things. He is bad at sports and at talking to girls. He has some skills and manages to graduate, attend technical school, and find a job at Bakersfield Optometry in his hometown of Bakersfield, California. Not long after Basil turns 22, his parents move to Tampa, Florida. Around the same time, Basil starts to feel that he is missing out on life. Desperate for a change, he secures a job as an optics technician at an observatory in Hawaii. The job entails watching and running the observatory atop a volcano. Though he will have to work weeklong solo shifts, Basil is unfazed.

When he arrives in Hawaii, he is energized by the new environment. Then he meets his coworker, Muriel MacDonald. She is a beautiful and intelligent young woman. Basil listens as she gives him a tour of the observatory. When she leaves, he is convinced he is in love.

Over the next five months, Basil's affections for Muriel grow. He and Muriel only spend one hour a week together when they swap shifts. Despite this deficit in time together, Basil believes that Muriel likes him too. One Sunday he hides 50 paper valentines around the observatory, and anxiously anticipates her delighted response. Instead, Basil gets a call from his supervisor saying he is fired for making inappropriate romantic advances.

Basil moves to Pocatello, Idaho. He gets a job at LensCrafters. Despite his attempts to start over, he cannot help thinking about Muriel and the volcano.

Eleven years later, Basil meets a woman named Mags Futrell. Not long later, they get married and buy a home together. Mags soon gives birth to a baby boy named Otis. For a time Basil feels that happiness is possible. He loves Otis, and devotes himself to fatherhood.

When Otis is five, Mags relapses and starts drinking again. Basil confronts her but Mags refuses to change. Upset by the tumult, Otis starts wearing a superhero cape. The doctor says it is a result of stress and that Otis will grow out of it. Three years later, Otis is still wearing the cape.

One night, Mags promises to change her ways and help Basil with Otis. While they are out, Basil makes dinner and browses the internet. He discovers an article announcing Muriel's bestselling book. He downloads the book and starts reading. He is disappointed to find no evidence of himself on the pages.

Mags returns home drunk. Otis runs to his room sobbing. Basil brings dinner to Otis's room and comforts his son. After cleaning up, Basil wonders if he should move with Otis to Florida. Then he sees Nicholas leave something on his doorstep. Nicholas is the contractor who is converting the old warehouse across the street into a mysterious business called The Master's Castle. On the step Basil finds two headlamps, a key to the castle, and a note from Nicholas.

Basil and Otis let themselves into The Master's Castle. They are delighted to find that it is an elaborate Putt-Putt course resembling a castle and castle grounds. Throughout the evening, Basil reflects and gains perspective on the past, present, and future.