An important element of this story is plot. When the Enterprise reaches Selva, the president of the colony explains that the Klingons live in the woods and occasionally attack and kill the colonists. Instead of exterminating the Klingons as the president wants, Captain Picard decides to try to befriend the Klingons and to arrange for peace. So Lt. Worf (a Klingon himself), Commander Data, and Councelor Troi go into the forest to accomplish that. They do befriend the Klingons, and learn that among the colonists is a traitor, tipping off the Klingons. And to top things off, they learn that the planet is violently unstable; the land surrounding the colony has been stripped of life only a few decades before it was settled. All these factors make for an exciting, suspenseful novel.
In addition to the plot, the setting is also important to the story. The story takes place on planet Selva, a planet torn between extremes. Forty percent of it is covered with glaciers. The oceans have a deadly acidic film covering them and are heated by underwater volcanoes. The colony is located in between the two extremes, near enough the water to benefit from the warmth but far enough away to avoid the storms near the oceans. The two extremes of this planet symbolize the relationships of the Klingons and colonists; both are separated by great differences.
No less important than plot and setting is theme. The author is trying to get across his belief that although peace is preferable to war, hatreds can run deep. Worf, Data, and Troi were able to buy the trust of the Klingons with food and luxuries the Klingons didn't have, with a reasonable degree of success. But after the atrocities the Klingons had committed, the least thing the colonists wanted was peace with them. This theme was the heart of the story, the reason the author wrote it.
The plot, setting, and theme were all important to this novel. The plot adds excitement and builds suspense. The setting "sets the stage for the plot"; it symbolizes the main factions of the planet. The theme demonstrates the author's view on war. For those who like Star Trek: The Next Generation, or just like exciting stories, War Drums is a book well worth reading.