Working to please his father, who was killed in an act of heroism, Stringship Vandenberg Captain Horse Cooke leads a small group of colonists and astronauts as they travel to create the most distant human outpost. They discover highly evolved life including the first two intelligent, non-terran species, one friendly, one not.
In the Groombridge 1618 system the humans find superintelligent "chewies," who resemble sea otters, and stand upright on land. They warn of an attack by orcs, the unfriendly sentient species. The quarter-tonne orcs have a near-human intelligence and are armed with weapons and use tactics like those of Alexander the Great.
The almost unarmed astronauts have little protection when hundreds of orcs attack. The 54 humans have no defense but killing many orcs, in direct violation of human laws to protect all species on other planets. After three attacks are repulsed, the Vandys improve the colonists’ defenses and return home where Horse learns that doing what is best is better than following the regs and rules, as he thought his father demanded.