"It might even be true. It was not for him to know. A man says something. Sometimes it turns out to be the truth, but this has nothing to do with the man who says it. What we say occupies a very thin surface, like the skin over a body of water. Beneath this, through the water itself, is what we see, sometimes clearly if the water is calm, sometimes vaguely if the water is troubled, and we imagine this vision to be the truth, clear or vague. But beneath this is yet another level. This is the level of what is and this level has nothing to do with what we say or what we see."
'Sarah Canary' is one of SF's most powerful explorations of the Other. Fittingly for a book about First Contact, it deals with alienation. But Sarah Canary doesn't act as a filter to give us a fresh perspective on humanity as much as a focal point that draws in the novel's motley crew of disenfranchised. Sarah Canary isn't really the protagonist; she doesn't actually do much, we never find out anything about her motivations or thoughts, and Fowler deliberately leaves her true nature ambiguous. She's a walking Outside Context Problem, and how the various characters perceive and react to her reveals the prejudices, concerns and fears of the 1870s America she mysteriously appears in.
The masterstroke of 'Sarah Canary' is not just in how it explores the lot of the disenfranchised, but also how it highlights the inhumanity of the society that allows this. The book takes us on a tour through Chinese labour camps, mental asylums, Indian shanty towns and carnival shows, emphasising that, unless you were a particular subset of straight white male, this was a time and place that granted you precious little rights. We meet Chin Ah Kin, who first discovers Sarah Canary, a Chinese immigrant who was more or less kidnapped and brought to the States to work on the railways. They are joined by B.J., an escapee from the asylum, which is run on a strict budget with little care for the patients' well-being and no meaningful way of treating them, and Adelaide Dixon, a suffragette who is routinely persecuted for daring to suggest that women should enjoy sex. All three of them perceive Sarah Canary differently, but all three of them try to help and protect her. Along the way they encounter a series of unpleasant white men who plan to exploit her one way or another.
All of this makes the book sound much more didactic than it actually is. 'Sarah Canary' is far more well rounded and complicated than that. Fowler deftly reveals the extent to which prejudice can divide people. Initially, Chin, B.J. and Miss Dixon view each other with the same hostility and suspicion that society faces the with, but through their shared experiences with Sarah Canary they gain both a mutual respect for one another as people and a profound understanding of each other's circumstances. Additionally none of the unpleasant white men are straw men. Fowler makes them well developed enough as characters that we are able to see where they are coming from, even if we don't sympathise. Frequently they too are in their own ways victims of a cruel and exclusionary society - for example Harold, perhaps the closest the book has to a villain, is revealed to have been driven to the brink of sanity following his experiences in a prisoner of war camp following the end of the Civil War.
One of the main themes of the book is perception - how our perception shapes the way we experience the world, and whether or not this prevents us from ever really seeing the truth. The quote above reminds me of Philip K. Dick's famous maxim, "Reality is that which, when you stop believing in it, doesn't go away". Here we have almost the opposite problem - when you can't separate out how your own beliefs colour something, how can you ever know what reality truly is? This links back to the theme of prejudice, and how the characters are in reality very different from how they are perceived to be. Chin has to deal with the possibility that he may be lynched wherever he goes, yet he is perceived as being dangerous. Miss Dixon is called a slut and a whore because of her campaigns for women's rights, yet she has barely had any experiences with men and is at heart a romantic. Everyone thinks B.J. is crazy, yet in the chapter where we get to experience his viewpoint we find out he is perfectly lucid, if oblique. This all makes it thoroughly appropriate that Sarah Canary herself is only perceived by others, so the truth as to who or what she actually is is never revealed.
Sarah Canary's true nature is only hinted at. Although it's possible to read the book as straight historical fantasy with no SF elements whatsoever, the juxtaposition of the alien and alienation is too resonant to ignore. Throughout the book she is compared or described in supernatural terms. She is also compared to a butterfly, specifically with regards to her mysterious transformation at the end, and from Chin's first encounter with her he associates her with the image of a one-winged bird. The combined vision we get from all these images perhaps gives us an idea of what her true form might be.