A thoroughly enjoyable first-contact story. It's not biologically plausible; the aliens are way too much like humans, in both appearance and chemistry; the idea that a whiff of alien pheromones would make humans horny is more than merely far-fetched. However, the uneasiness caused by similar-yet-different is crucial to the story, as is the confusion of attraction. Although the alien psychology and culture are pretty well-developed, the real attraction is the reflections on humans; also, the Belfast setting is incredibly vivid. I know nothing of that city and very little of Irish politics (seems like it's diverging very rapidly from what might have been predicted when this book was written hardly more than ten years ago); but Nicholas Whyte, a native of Belfast and a political analyst by profession, says that this book is a favorite of his, which is more than enough for me.