"Big Black Good Man" begins on a warm August evening in Copenhagen, Denmark. The exact year isn't mentioned, but the setting aligns with the late 1950s, when the story was written. Olaf Jenson, the night porter at an inexpensive hotel frequented by sailors and students, is in his office. The following day, Jenson will turn sixty. As he finishes a beer and smokes a cigar, he reflects on his simple and uneventful life.

It's late, and Jenson is about to take a nap when an enormous black man enters the office and requests a room. Stunned by the man's size, Jenson doesn't respond until the man repeats his request. Jenson inquires if the man is American (yes) and a sailor (yes). Although Jenson doesn't consider himself prejudiced, he thinks, "this particular black man . . . Well, he didn’t seem human. [. . .] There was something about the man’s intense blackness and ungamely bigness that frightened and insulted Olaf."

Jenson wants to deny the man a room but is too afraid to do so. Once he agrees to accommodate him, the sailor hands Jenson a roll of fifty- and one-hundred-dollar bills to store in the safe. Struggling to find a way to remove the man from the hotel, Jenson plans to say that rooms aren't available for just one night. However, the man states that he intends to stay for five or six nights.

The man declines Jenson's offer to carry his suitcase, but Jenson leads him to his room. The man requests whiskey and a woman, which are typical requests at the hotel. Still disturbed by the man, Jenson returns to the office and reluctantly calls Lena, a prostitute who frequently visits guests there. He warns Lena about the man's size, but she is unfazed and arrives shortly. Jenson worries about her while she is with the man, but she later leaves, first giving Jenson his share of her fee.

On the following night, the man returns late and asks for Lena by name. This routine continues for six nights. Then, the man visits the office to settle his bill and retrieve his money from the safe. He gives Jenson a tip. Instead of leaving right away, he stares at Jenson, who grows increasingly terrified. Finally, the man instructs Jenson to stand. He then approaches and places his hands around Jenson’s neck, smiling. Believing he is about to be strangled, Jenson urinates on himself. The man moves his fingers gently on Jenson’s neck and then withdraws them. Jenson begs the man not to harm him, to which the man responds, "I wouldn’t hurt you, boy. So long."

After the man leaves, Jenson breaks down, overwhelmed by humiliation, fear, and anger. He regrets not using the gun he keeps in his desk drawer to kill the man. He contacts the hotel owner, claiming he's unwell, and she comes to take over, allowing Jenson to go home and change out of his soiled clothes. He also lies to his wife, telling her he's sick.

Throughout the following year, Jenson is haunted by the fear of the man's return and indulges in vivid fantasies of revenge. He envisions the man's ship sinking in a storm, imagining him drowning "gasping and choking like a trapped rat," with his decaying body eventually devoured by a white shark.

One year later, on an August night, the man reappears. Jenson informs him that there are no rooms available, but the man says he doesn't need one. When Jenson inquires about his intentions, the man grins, opens his suitcase, and retrieves something. He approaches Jenson and...