Christopher is a young, aspiring detective living in London in the 1930s. He spent his early childhood in the International Settlement in Shanghai before being abruptly orphaned at age nine when both his parents vanished. Deeply driven by a desire to solve the mystery of his past, he dedicates his life to investigative work. He often feels like an outsider in English society and struggles to form lasting connections.

Akira is a young Japanese boy living in the International Settlement in Shanghai. He struggles with his cultural identity, feeling alienated after a brief attempt to continue his education in Japan. Adventurous and willful, he represents a sense of safety, loyalty, and belonging for Christopher during their childhood years.

Sarah is an ambitious young woman who frequently attends high-profile parties in London. Having lost her parents early in life, she seeks meaning by attaching herself to men of influence, hoping to help them change the world. She faces societal disapproval for her forthright nature but remains fiercely determined to make an impact.

Uncle Philip is a close family friend and a business partner to Christopher's mother. He runs a philanthropic organization and campaigns against the opium trade in China. To young Christopher, he is the ultimate model of an English gentleman, offering the boy attention and affection when his own father is preoccupied.

Christopher's mother is a captivatingly handsome woman living in the International Settlement in Shanghai. She is a passionate campaigner against the opium trade facilitated by European companies, which puts her at odds with her husband's profession. Her strong moral stance and sudden disappearance heavily influence Christopher's development.

Christopher's father is an employee of a large European firm responsible for importing opium into China. He is a generally modest man who feels inferior to philanthropists like Uncle Philip. He worries constantly about his financial standing and his family's ability to return to England. His sudden disappearance is the inciting mystery of Christopher's life.

Jennifer is a young orphaned girl whose background echoes Christopher's own traumatic childhood. Christopher decides to become her guardian in 1934. She is quiet, composed, and eager to be helpful, seemingly attempting to earn her place in the world through good behavior.

Sir Cecil is an older, distinguished public figure who believes he can help negotiate peace in China during the global conflict. He marries the younger Sarah Hemmings, who hopes to spur him on to greatness. Despite his lofty goals, he struggles heavily with alcoholism and gambling addiction.

Colonel Chamberlain is the man who chaperoned the nine-year-old Christopher on his boat journey from Shanghai to England. He views England as Christopher's rightful home and remembers the young boy as moody and tearful, a description that irritates the adult Christopher.

James is Christopher's old school friend from the University of Cambridge. He is well-connected and remembers Christopher as an "odd bird" who awkwardly copied others' mannerisms to fit in, a memory Christopher finds embarrassing.

MacDonald is an official at the British consulate in Shanghai. Christopher firmly believes him to be a senior intelligence officer who can help him arrange a meeting with a notorious communist traitor to aid in his investigation.

Mr. Grayson is a representative from the Shanghai Municipality Council. He cheerfully insists on organizing a welcoming ceremony for Christopher's parents, seemingly ignoring the grim reality that they are still missing.

Anthony is a former school friend of Christopher's from England who now lives in Shanghai. He assumes he and Christopher share a bond of having been lonely, miserable schoolboys, which offends Christopher's carefully constructed self-image.

Inspector Kung is a once-famous Shanghai detective whom young Christopher idolized as an unmatched hero. Years later, he is found living in squalor at the Inn of Morning Happiness, having fallen victim to opium addiction.

Wang Ku is a Chinese warlord involved in the opium trade. Christopher remembers seeing him in his childhood home dressed in traditional garb shortly before his mother's disappearance, recalling his mother yelling at the man.

Etsuko is Akira's older sister. She enforces traditional behavior and scolds Akira when he misbehaves or steals from the family's servant.

Ling Tien is an old Chinese servant working for Akira's family. He becomes a figure of terrifying fascination for the boys, who invent elaborate fantasies about him keeping severed hands in his room.

Miss Givens is the nanny Christopher employs to provide daily care and supervision for his newly adopted ward, Jennifer.