There is an interesting side-bar to the tale of this book, one that I learned only relatively recently. When the BBC was deciding what to produce as a Saturday early evening SF serial in 1962-3, they has four choices. One was a new original series called "Doctor Who" and the other three would have been adaptations of existing SF novels. The running favourite was Three to Conquer, which they said was written "unusually well and with a good sense of humour" - how different life for EFR's works could have been.
The book itself again crosses genres, as its style is transatlantic, not dissimilar to a 1950s crime novel in feel, but definitely an SF invasion story with an intelligent twist. The characters are real, the dialogue works and flows in a believable way and the plot unfolds swiftly and relentlessly towards the satisfying resolution. It is very cinematic in style as well, and would indeed lend itself to TV or film production.
No revealing of the plot. This is another gem to discover and I'm not going to spoil it for you. My best suggestion is read the book. You will not regret doing so.
