Alek is the fifteen-year-old son of Archduke Franz Ferdinand and his common-blood wife, Princess Sophie. Raised as a prince but holding no official title due to his parents' morganatic marriage, he struggles with his identity and authority. Over the course of his escape, he learns to operate heavy machinery and begins to form his own moral compass. He changes from an entitled boy to a young man capable of making difficult leadership decisions in the face of a global conflict.

Deryn is a brave fifteen-year-old girl from Scotland with a deep passion for flying. To pursue her dream and avoid a traditional Victorian woman's life, she disguises herself as her fictitious male cousin, Dylan, to serve as a midshipman in the British Air Service. She is a quick-witted and compassionate airman determined to prove herself aboard the famous airbeast Leviathan.

Volger is Alek's fencing master and a longtime confidant of Archduke Ferdinand. He presents a harsh exterior and frequently antagonizes Alek about his common blood. This demeanor masks his deep devotion to protecting the young prince. He serves as Alek's primary mentor and utilizes strict pragmatic methods to ensure the boy's survival.

Dr. Barlow serves as a prominent scientist, diplomat, and head keeper of the London Zoo. As a powerful figure in a male-dominated field, she commands immense respect aboard the Leviathan. She is highly observant and subtly gathers information while carrying secret cargo meant to impact the war effort.

Klopp is the master of mechanics for the Hapsburg family and Alek's piloting teacher. A commoner by birth, he provides a contrast to Volger's strict mentorship by offering Alek gentle guidance. He is fiercely loyal and willing to sacrifice his own rank to ensure Alek's safety.

Newkirk is a midshipman and friend of Deryn's in the British Air Service. He identifies as a Monkey Luddite, meaning he feels uncomfortable around the Darwinists' fabricated beasts, but he serves in the Air Service because he believes the sky is the safest place during a war. He eagerly anticipates combat against the Clankers.

Mr. Rigby is the bosun aboard the Leviathan. He is directly responsible for training and managing the midshipmen. He is a steadfast and experienced airman who leads his young crew during dangerous combat situations and feeding drills, ensuring they maintain discipline in the air.

Bauer is a young corporal who serves as part of the five-man crew operating the Cyklop Stormwalker. He assists Klopp and Volger in their mission to smuggle Alek out of Austria-Hungary, manning the machine's weaponry during combat encounters with German forces.

Hoffman is an engineer and member of the stormwalker crew tasked with keeping Alek safe. He works closely with Klopp to maintain the complex, top-heavy Clanker machine as the team navigates treacherous terrain and enemy fire.

Jaspert is Deryn's brother. He aids his sister in her dangerous plan to join the British Air Service by providing her with his hand-me-down uniform and introducing her to recruiters as his male cousin. He risks prison time to help her achieve her dream.

Archduke Franz Ferdinand is the heir to the Austro-Hungarian throne. His morganatic marriage to a commoner complicated his line of succession. His tragic assassination serves as the catalyst that sparks a global war and sends his son into hiding.

Princess Sophie is the common-born wife of the Archduke. Because of her unequal rank, her marriage to the Archduke meant her children were not legally permitted to inherit royal titles, a political reality that shapes her son's life before her assassination.

Emperor Franz Joseph is the 83-year-old ruler of Austria-Hungary. Though he does not directly interact with Alek during the early stages of his flight, his advancing age and the political vacuum his potential death creates drive the urgency of Alek's escape.

Tazza is Dr. Barlow's pet thylacine, also known as a Tasmanian tiger. Though unusual in appearance and capable of jumping like a kangaroo, the creature is an entirely natural animal serving as a companion to the prominent scientist.

The Captain is the commanding officer of the Leviathan. He oversees the airbeast's crew and manages the ship's demanding military and diplomatic missions. He makes difficult tactical decisions during combat and manages the competing interests of his high-profile passengers.