There is a deep tone of honesty and directness in this book, akin to that of Jenny Randles, and the evidence is presented directly, often in direct quotations from eyewitnesses. There is some reliance on hypnotically extracted accounts of abductions (never to be trusted too closely), but not enough to dissuade us from seeing that something is going on. The question is still: "What is it?" The authors leap well beyond the evidence they've offered in trying to answer this, with the tired and culturally-conditioned answered "Pleiadeans" and "genetic manipulation" and "weapons technology" answers.
There are surely deeper answers, perhaps even deeper than human comprehension, and the Imbrogno/Horrigan answers often border on the silly.
Do intense electrical fields open interdimensional doors? If so, then stars and black holes must be utterly bewildering confusions of dimensional interleaving. Has American weaponry put ET's technology to use? If so, how come we still go to war with battleships and bombers instead of "appearing", irradiating, and vanishing?
The authors admit to being believers. I believe, too, that thousands of highly credible witnesses cannot be lying, and I believe they have seen something non-human. But Imbrogno/Horrigan have not presented the detailed additional evidence that would permit the rather more outrageous elements that percolate through their conclusions.
By the way, they confess to being materially delayed in researching the Belgian Air Force sightings because they were documented (gasp!) in French. Good researchers should have several tools available, including a few foreign languages or at least a friend or two who can handle Europe's second-most-common language and North America's third-most-common. This complaint was out of place in a book claiming to do intelligent research. Get with it, folks!