Whitley Strieber claims to be an abductee -- a person taken by aliens against their will for their own unknown reasons. Strieber, a talented author in both fiction and non-fiction, admirably peels back the layers on a few mysterious evenings in his life and finds a lot more than he bargained for. Strieber previous to this was not interested in the subject of UFOs at all. In order to read this book, one must accept Strieber at his word. He is the first to admit that his recollections may be flawed, but here they are stripped bare.
I found the most chilling aspect of Communion to be the transcripts of hypnosis sessions. These are truly terrifying and it is easy to imagine what Strieber saw on those nights, so clear are the descriptions.
Most important here are the descriptions of Strieber's actual encounters. When taken at face value they mesh perfectly with other accounts, and are hard to dismiss. If one digs deeper, there is very little here to sooth the questioning mind -- merely more questions. Strieber never discerns his visitors' intentions. There is a common theme of apocalyptic warning (which apparently inspired Whitley's earlier novel, Warday) but not much else to divine exactly what these visitors are here for, or even where they come from.
The other books in this series are not essential. This is the one. Get it. You should be able to polish it off in a couple days, it is a page-turner!