This is one of the best science fiction stories ever written. Several years before the tale begins, an alien race called the Aalaag arrived on the Earth and easily take control. Their technology was so far advanced over humans that all military resistance was futile, the most advanced human technology could not even reach the level of scratching their paint. The Aalaag are also a species with a strict code of honor, and their goal is to harness the resources of Earth to build the Aalaag strength so that they can eventually reclaim their worlds. Many centuries before, an even stronger species had taken over the Aalaag home systems, forcing them to flee out across space, looking for new places to live.
While the presence of the Aalaag has brought an end to war between humans and created a very ordered society, the Aalaag mentality is such that the humans are considered to be the equivalent of cattle. The main character, a linguist named Shane Evert, is one of the few humans capable of speaking and understanding the Aalaag language. He is a translator for the Aalaag governor of Earth, in some ways one of the highest ranking humans on Earth.
As the story begins, he witnesses an Earthman being killed by the Aalaag for an act they consider rebellion. An Aalaag youth unintentionally injured the man's wife so he attacked the Aalaag with his bare hands. According to Aalaag law, the man must immediately be put to death by being impaled on spikes and all humans in the area forced to watch until the man is clearly dead. Evert is repulsed and draws an image of a cloaked man with a staff under the dead man. With this act, he takes the first step in becoming the pilgrim, the worldwide symbol of human resistance to the occupation.
However, he knows that any overt resistance against the Aalaag is futile, so he must find a way to fight back without overtly challenging the Aalaag. As his plan develops, he creates a worldwide network of resistors, which grows to include the covert security services of the major nations. They all cooperate to prepare for the day when humans finally challenge the power of the Aalaag.
Shane uses his knowledge of the Aalaag to convince the governor that they will achieve no real value if they continue their hold over Earth. He is genuinely surprised when the Aalaag governor agrees and they abandon Earth without destroying any structures or killing any humans.
What makes this story so powerful is the interaction between the alien race and the humans. Even though the Aalaag governor and Shane talk at length about their differences and their similarities, and do find some common ground, in the end the governor still considers the humans to be ungovernable cattle. Dickson is superb in creating an ending that gives you pause. Instead of a joyous triumph at the human "victory" over such a powerful foe, it is very bittersweet. Human national rivalries resurface even before the Aalaag are gone and you think deeply when Evert is told that the reason the Aalaag are leaving is because they consider the human species to be unworthy. Despite their actions of enslaving the human race, the Aalaag are very honorable beings, and they have many admirable qualities.