I enjoy Eric Frank Russell's stories as a whole, but Sentinels from Space is far from my favorite. It has very little of the classic Russell humor and a moderately interesting plot.

Humanity has developed several different kinds of mutants, mostly due to space travel. Most of the known ones live on Mars and Venus, since everyone there has ancestors who traveled through space, whether or not they themselves have done so.

Mars and Venus are looking to establish their independence from Earth. Certainly any American citizen can sympathize with the desire to not be ruled by a distant power, at least if he or she has an understanding of history. But in this case, a war between the three worlds is inadvisable, even though no human knows it.

Yes, Earth, Mars and Venus are watched over by alien sentinels, who know that such a war is not a good idea, as alien invasion is a very real future problem. They would prefer to keep the planets united, and not allow Earth to be ruined, as it easily could be in such a war.

I found the range of mutants quite interesting and creative. Beyond the usual telepaths and teleports, there are "insectivocals" who can speak to insects, and other such mutations. I'll give some points for creativity, but still, this isn't one of Russell's stories that I will reread often.