A collection of story stories from his Polesotechnic League universe.
The frame story is that a Yrthian, after his mother, who wrote The Sky Book of Stormgate about their speices, died before she could do a human companion work, wrote the work she intended. It gives the story introductions a certain -- flair. Especially the metaphors. (Yrthians are winged.) This was for a colony called Avalon, founded by both humans and Yrthians.
The stories cover a range. The first one is first contact with Yrthians from the human point of view. The last two are incidents on Avalon itself. They cover not only all sorts of points in between but all sorts of places there. "How to Be Ethnic In One Easy Lesson" takes place on Earth; "The Man Who Counts" (elsewhere also known as "The War of the Wingman") and "Season of Forgiveness" take place on planets appearing in no other story.
Nicholas van Rijn and David Falkayn appear in some.
The quality varies. I skipped "The Problem of Pain" and "Day of Burning" myself, but "Season of Forgiveness" is quite possibly the best SF Christmas story.