I see a larger meaning in the doctor's "straight course" for the Custom House, despite the Custom House being an "ugly enormity." Animated by his love for Mrs Gould, the doctor is now acting on behalf of an ideal; he is trying to assure her safety until Charles Gould can somehow triumph and establish organized society around her. At the same time, his cynicism recognizes organized society as an "ugly" self-flattering vanity. He is thus "lonely" because he is the only protagonist now acting in the name of an ideal (higher than simple greed or power), but the "broken wing," denoting the limp from his tortures, also represents his remaining cynicism.

The sunset corresponds to his dream-ideal of love for Mrs Gould.