In Stephen King's Pet Sematary, identify the antagonist, the theme, and the conflict (e.g., man vs. man, man vs. self, etc.).

There are potentially two antagonists of Pet Sematary. The first and most clear antagonist is Gage. While Gage is an innocent child during the first part of the book, he becomes the main antagonist in the second part of the book. Gage causes significant harm to Louis by killing friends and family members and by forcing Louis to ultimately kill Gage. In a more indirect sense, the antagonist can be seen as the cemetery itself. The pet cemetery brings people and animals back from the dead, but as Jud notes, the malevolence exhibited by Church is the rule rather than the exception. The pet cemetery lures individuals struggling with grief to its grounds for a chance to defeat death and responds by sending evil beings out into the world. In this sense, the pet cemetery could be seen as a malevolent being who preys on grieving individuals in order to increase the grief in others.
The theme of this book is death and the destructive nature of grief. The plot of the novel centers around the deaths of Church and Gage. Jud's wife also experiences a near death experience, and Rachel has significant issues dealing with death because of the traumatic death of her sister during childhood. Death is ever present throughout the novel. However, if death itself were the only issue, then this would likely have been an interesting work of literary fiction. The horror in the novel comes from the destructiveness of Louis's grief. He is unable to deal with the prospect of Ellie's grief after the death of Church, leading him to resurrect the cat by using the pet cemetery. Later, after learning of the negative ramifications of resurrection, Louis still decides to attempt to resurrect his son. This is done solely because Louis cannot deal with his own grief after Gage's death. Finally, even after the destruction caused by a resurrected Gage and Church, Louis is still unable to deal with the death of his wife and attempts to resurrect her.
The overt conflict in this novel is man versus the supernatural. The resurrection of Church and Gage pits Louis against supernatural beings. However, the true conflict in this novel is man versus death, with the added statement that death always wins. Louis repeatedly works to stop or nullify death throughout the novel. All of his attempts result in more death, so in attempting to defeat death, Louis actually causes more deaths.