Devlin is an Irish-born baggage handler at Heathrow Airport who maintains a highly structured, predictable routine. He previously worked as a busker traveling across Europe but retreated into a life of strict stability following a tragic personal loss. He finds the mysterious violin in the airport's lost and found, an event that forces him out of his complacency. He struggles with a profound disconnect from his current girlfriend, Melissa, specifically regarding their contrasting priorities and views on social media.

Gabrielle runs Wilding's, a fine instrument appraisal shop she took over from her father. Formerly a highly promising violin student, she suffers from chronic, unexplained wrist pain that forced her to abandon her performance career. She maintains a frosty, professional exterior to protect herself from further emotional pain. She spends her free time searching for lost pieces of music, specifically works by Niccolò Paganini.

Walter is a retired history teacher living alone in London. Having never married or formed close attachments, his retirement leaves him feeling aimless and profoundly isolated. He attempts to form connections with his neighbors but continually faces rejection. He desires a sense of purpose to combat his growing depression until Devlin arrives at his door.

Verity is a silver-haired antique shop owner based in Montreal, Canada. She grew up under the strict control of an abusive father who originally owned the business. She hires criminal elements to track down a specific stolen violin, willing to use threats and extortion to recover the item her father lost decades ago.

Clara is the second daughter of a wealthy Irish family in the early 19th century. She possesses a stunning singing voice, which she is strictly forbidden to use indoors due to her older sister's jealousy. She prefers the freedom of the forest, where she can sing without restriction.

William is a 19th-century Irish carpenter who dreams of becoming a master luthier. He is highly focused on his craft, aiming to build instruments that capture the eternal beauty of birdsong. He lacks the refined manners of the upper class but speaks with a direct honesty.

Melissa is Devlin's girlfriend of several years. She focuses heavily on curating an aesthetically pleasing life for social media and strongly desires a traditional progression in her relationship. She feels immense frustration over Devlin's ongoing hesitation to commit to marriage.

Gregory is Gabrielle's father and the former owner of the fine instrument appraisal shop. He financed and supported his daughter's extensive musical education during her youth. His business decisions left a lasting impact on Gabrielle and the shop's current reputation.

Max is an acclaimed violin soloist and highly respected tutor in the classical music world. He instructed Gabrielle, pushing her intensely toward greatness. His demanding instruction style left a lasting, traumatic impact on her life.

Ursula is Clara's older sister in 1812 Ireland. She is highly conscious of her social standing and prospective suitors. She actively suppresses her younger sister's talents out of a fear of being overshadowed by Clara's natural gifts.

A fictionalized version of the real 19th-century maestro. He is an extremely gifted, innovative violinist who actively pushes the boundaries of musical norms. He encounters William and becomes fascinated by the unique instrument the luthier carries.

Roger is an expert in dendrochronology based in Bristol. He previously studied music alongside Gabrielle. Their friendship became highly competitive and eventually faded completely after she stopped playing the violin.

Trudy is Gabrielle's therapist. She works patiently to help her client break through deep emotional barriers and dissociation, though she often meets stubborn resistance from Gabrielle.

Pete is Devlin's coworker at the airport. He oversees the lost property section and facilitates Devlin's purchase of the mysterious violin before it goes to public auction.

Summer was an Australian exchange student who met Devlin while he was busking on Grafton Street. Her memory heavily influences Devlin's current lifestyle, specifically his complete avoidance of music.

Lord Ravenshaw is the descendant of Margot Clement, the heiress who previously owned the stolen violin. He resides at Larkfield Hall and maintains a highly detached attitude regarding his family's lost property.

Margot Clement was a wealthy heiress who lived to be 104 years old. After her death, authorities discovered the highly valuable violin in her London apartment.

Sofia is an art history professor and formerly a shady art dealer. She taught Verity how to deal in stolen and forged art but has since given up her criminal past to live quietly.

Achille is the son of the famous composer Niccolò Paganini. He takes custody of the violin following his father's passing, promising to carry out his father's final wishes.