Sibling Rivalry
Sibling rivalry is usually confined to the more harmless elements of family life; who gets the most touchdowns on the football field, for example, or even who gets the most Cheerios in their cereal bowl in the morning. The Story of Edgar Sawtelle takes sibling rivalry to its more murderous extremes. Claude is jealous of Gar, for a multitude of reasons, starting with his closeness to their parents and his natural ability to raise dogs, an ability that Claude does not have in such abundance. He envies him his family too, particularly his wife, whom he wants for himself, and with whom he ultimately has a relationship.
After he murders Gar, Claude assumes his life as his own. He moves into the farmhouse, he takes up with Trudy and he acts to all intents and purposes as the lord and master of all he surveys. The result of the rivalry between the brothers is tragedy, because at the end of the story, both brothers, and the only heir to the dog breeding enterprise, are all dead.
Duplicity and Murder
The book has a number of murders in it, those committed by Claude being completely premeditated and the result of a great deal of scheming and duplicity. He and his brother argue a lot and he takes the opportunity after one of these arguments to kill Gar, using a syringe filled with poison. He then hides the syringe but when it is discovered plans on killing Edgar, because he discovered it, as well.
Claude then decides to try to get rid of Edgar, using any means necessary. At first it appears that he will not have to resort to violence, because Edgar accidentally killed the family veterinarian who just so happens to be the father of the local police detective. A few suggestions as to the identity of the perpetrator in the police officer's ear, and it seems that Edgar, now the chief suspect in the death, will be questioned, arrested, and taken away from the farm, protecting Claude's duplicity from discovery. However, when Edgar discovers the poison too, Claude knows he has to get rid of him sooner rather than later and sets fire to the barn on purpose, hoping that Edgar will die in the blaze.
Signs from the Afterlife
Gar appears to guide Edgar from beyond the grave, and also ultimately to have a hand in Claude's death. Edgar sees his father;'s ghostly outline whilst he is in the barn, and feels that his father leads him over to the place where the syringe filled with the poison that killed him has been hidden. Gar is clearly trying to identify his own murderer to the living. When the barn is on fire, and Claude is trying to escape from it, Gar also prevents him from doing so by filling the barn with smoke and making it impossible for Claude to find his way out. This suggests that he is exacting his own justice on his brother.