·       Osla Kendall: The protagonist of the novel, a young woman from a wealthy family who is recruited to work at Bletchley Park, the British codebreaking center during World War II. She is a kind and compassionate woman who is determined to make a difference in the war effort. She is also a brilliant mathematician who is determined to crack the German Enigma code.

·       Mab Churt: Osla's best friend from boarding school, who is also recruited to work at Bletchley Park. She is a kind and compassionate woman who is determined to make a difference in the war effort. She is also a brilliant linguist who is determined to crack the German Lorenz code.

·       Beth Finch: A young woman from a working-class family who is recruited to work at Bletchley Park. She is a kind and compassionate woman who is determined to make a difference in the war effort. She is also a brilliant mathematician who is determined to crack the German Enigma code.

·       Dilly Knox: A brilliant mathematician who is the head of the Enigma codebreaking team at Bletchley Park. He is a kind and compassionate man who is determined to crack the German Enigma code. He is also a bit of a loner who is not afraid to speak his mind.

·       Maxwell Knight: A British intelligence officer who is in charge of the Special Operations Executive (SOE). He is a brilliant and charismatic man who is determined to win the war. He is also a bit of a rogue who is not afraid to bend the rules.

·       Prince Philip: The Duke of Edinburgh, who is married to Princess Elizabeth. He is a kind and compassionate man who is determined to support his wife in her role as Queen. He is also a bit of a mystery to everyone, including himself.