A fairly short science fiction story which aged badly. An alien race is searching for a better place to settle, and our own Solar system looks like perfect fit. There is a slight problem with native population - us humans, but it is nothing good weapons cannot solve: the humans do not have adequate defense/offense systems.
So, a survivor of one of attacks who also happens to be a millionaire scientist (when was the last time we had some of these in real life; Iron Man does not count) takes on himself to create a weapon capable of dealing with the threat. Obviously, his initial models are failures; the aliens also show they can adapt.
Mercifully, this book is short. The pseudo-science used in description of what the human savior is doing is laughable even for people whose only expose to physics was in the high school. The description of the last "ultimate" weapon made me laugh out loud, but I need to mention I took university-level physics class.
The characters are one-dimensional; the plot is completely 100% predictable. The ending is not believable even without the above-mentioned weapon. Still the book is entertaining enough (and it is free from Project Gutenberg) to warrant 2 stars.