Dark Harbor opens as the speaker—possibly an autobiographical representation of Strand himself—leaves his home and "the town to the others," walks down Main Street, and watches for the "great space that he felt sure / Would open before him." He begins to consider words and passages, metaphors and familiar tropes, weighing them to determine their worth. He considers words like a painter considers colors. Although he must turn up his collar against the elements, it is just now that he "beg[ins] to breathe."

The night seems to have no end, but the poet is wearing a white suit that shines; he stands out. He joins "the others"—perhaps other poets—at the station, and they prepare to travel out into the night. The others see the moon as a hindrance—they need the darkness, it seems—and they feel that the body itself is "worthless and only goes so far." It is limited, whereas imagination is not. They believe that poets are able to journey to places the rest of humanity cannot. The poets dream of becoming like angels, released from daily duties and cares, keeping company with one another and everyone "stunned into magnitude." They dream of being remembered, of making a difference. The speaker does not fit in with these other poets, but it is clear that he still feels a connection them.

The poet feels unworthy and struggles with self-doubt. He must come to terms with his past and with the differences in the way he sees life, and he must imagine his future. It is hard to feel satisfied. He feels his loves and griefs, it seems, more deeply. He fears that he has "lived in vain," that his work will have no effect nor make an impact on the world. He struggles with how to capture pain in words and how to do it justice, and it is the same with pleasure. He must contend with his own mortality.

In a world where heaven does not exist, "all is farewell." Even if people fail to acknowledge this or recognize it, they are always saying goodbye. The speaker imagines his future as an old man; he imagines how it will feel to be separated from friends and be devoid of relevance. He remembers his youth, his rampant sexuality, and knows that both are gone now. It is difficult to fit life onto the page, to maintain a "precision" and "Balance." He feels that he writes for himself alone, that "'not much listens'" to him, though he "feel[s] better for trying." The poet wonders if, after he's gone, he will find that he "live[s] against time, that the silk of the songs / I sang is not lost?" Or will he find that he's been forgotten? That what he "sing[s] is a blank," that none of it mattered anyway? This is, perhaps, the most frightening prospect. He finally finds himself in the company of other poets, some of whom have already passed away. He feels accepted among them. One of them, he notes, is "an angel, one of the good ones, about to sing." The speaker realizes that it is possible, then, to leave a lasting impact on the world.