War
The story in the novel takes place against a background of World War One. War is the central theme of the book and, therefore, the starting point for many of the other themes in the book.
The theme of war is illustrated by the depictions of the harshness of the war, the terror felt by the soldiers, and the decimation of a generation of young men caused by sending them off poorly equipped and with minimal training, to violence and probable death in the trenches. The theme also deals with issues such as the irony of the War Office knowing that certain battles were lost but continuing to fight them anyway for propaganda and morale, and of the fresh recruits getting progressively younger as the number of men able to serve in the war starts to dwindle. Overall, the novel depicts war as violent and horrifying.
Loss
Much of Tommo's experiences, good or bad, stem from the loss of his father and the way in which he deals with that loss. Beyond the emotional consequences of losing a parent, this loss extends to practical consequences: Tommo's home was tied to his father's job, and so the loss of his father also threatens the family's ability to preserve their home. Eventually, this is resolved, but then Tommo must deal with the trauma of war and the execution of Charlie, another kind of loss.
Blame
Another constant theme of the book is blame: both self-blame and blame from others. Because Tommo believes he caused the accident that resulted in his father's death, he blames himself for it. He hides this secret for his whole life until Charlie's execution, at which point Charlie reveals that he and the rest of the family knew this secret all along but never blamed Tommo for this because they knew it was entirely out of his control.
There is also a culture of blame within the army. Charlie is blamed for being a deserter when he tries to protect his brother and stand up to an inane order; in contrast, no one suggests bringing charges against Hanley for getting the young soldiers killed. There is also the question of blame when Molly becomes pregnant with Charlie's child before they are married—Molly's parents and the Wolfwoman blame Charlie, though they maintain that it reflects poorly on Molly as well. In fact, the two were in love and had plans to get married, which they did once they knew the baby was coming.
Bullying
Throughout the book, Tommo deals with numerous instances of bullying: people in power using their influence in pointlessly cruel and petty ways. Grandma Wolfe's treatment of the children is cruel; she insults and hits them constantly. The Colonel is an incompetent and cruel man, constantly threatening the Peaceful family with eviction unless they follow his whims. Later on, in the army, Sergeant Hanley targets both Tommo and Charlie as objects of his bullying, and when he realizes that Tommo is underage, he targets him all the more. The book also deals with the problem of standing up to bullies, which is nearly impossible as the boys are powerless in each situation and they would find themselves punished all the more terribly if they were to try to stand up for themselves. Notably, Charlie frequently stands up to instances of bullying (such as in Mr. Munning's classroom and in the army), and he eventually dies because of this after he is accused of desertion.
Love
There are many kinds of love in this novel. The main one is probably the brotherly love between Charlie and Tommo. Charlie takes many risks to help Tommo—for instance, when Tommo is being beaten up by the student in his class, Charlie stands up for him, despite the fact that this action will get him in trouble. During the war, he even helped Tommo to survive, even though he ended up getting executed.
Another form of love is the familial love between the members of the Peaceful Family, especially Mother and Big Joe. Though Big Joe is disabled, he is gentle and loyal, and when Molly declares she likes Big Joe, Tommo decides that he will love her forever. The unrequited love between Tommo and Molly is more complicated; at the end of the novel, Tommo goes to fulfill the promise he made to his brother of looking after Molly and the child, but it is not clear what their relationship will be, nor if Molly will grow to love Tommo the way that she loves Charlie.
Loyalty
The nature of loyalty is a major theme in the book. The Peaceful family members are deeply loyal to each other and to Molly as well, taking her in after her parents realize that she is pregnant and welcoming her fully. Despite their loyal service to the Colonel, their loyalty is not paid back, and the Colonel repeatedly threatens to evict them from their home. Charlie is profoundly loyal to Tommo, staying with him even when he is told by Hanley that this will result in a court-martial for him. Previously, Charlie demonstrated enormous loyalty when Captain Wilkie was injured and ordered the ‘skittle team’ to return safely with the captured soldier: Charlie refused this order and carried Wilkie back with him. Overall, Charlie is an exemplar of loyalty throughout the book.
Bravery and Cowardice
Many characters demonstrate bravery in this novel. Tommo shows bravery by joining up for war in response to the old woman who calls him a coward, despite the fact that he is underage and should not be going to war. At the beginning of the novel, Tommo's father expresses courage by saving his son from a falling tree, giving up his own life in the process. Later, Charlie demonstrates courage in numerous ways: by standing up to the cruel Mr. Munnings, by rescuing the elderly dog Bertha when the Colonel threatened to shoot her for being old, and by staying with his injured brother Tommo even when it meant he was accused of desertion. Tommo shows his own form of courage as well, enlisting in the army to prove the elderly woman who'd accused him of cowardice wrong. Bravery is also shown by Charlie when he is told he will be given a death sentence for desertion but still chooses to stay with Tommo.
Cowardice, the flip side of bravery, is also shown in this novel. Tommo demonstrates cowardice when he refuses to confess his feelings for Molly. Despite much tension and many exchanges of kisses, Tommo still does not reveal his feelings for Molly. Charlie beats him to it and ends up having a baby with Molly.
The novel also subverts expectations regarding deserters. Though desertion is frequently considered a crime of cowardice and being unwilling to face the rigors of battle, it is clear from this novel that sometimes, those people accused of desertion were, in fact, acting with great courage. Charlie refuses to risk the life of his injured brother and the men around him, and he refuses Hanley's order to make a charge. Though this is, in fact, a courageous act of standing up against a bully who is abusing his power, Charlie ends up accused of cowardice and desertion.
Injustice and Justice
The themes of justice and injustice run through the novel. Charlie frequently takes a stand against injustice, whether it is the Colonel threatening to put a beloved dog to death or a commanding officer who makes poor decisions. Charlie frequently suffers for his choice to stand against injustice. For example, Hanley’s orders to leave the shelter are suicidal and lead to the deaths of many, and Charlie fearlessly points this out while also remaining with his wounded brother Tommo, who cannot possibly stand, let alone run. Despite the fact that Charlie is correct about the fact that this poor choice will lead to men's deaths, Hanley accuses Charlie of being a traitor and eventually achieves his execution.
The end of the book states that many WWI soldiers were executed for desertion with short trials under shady circumstances. The novel leaves readers questioning if these executions were just or not.
