Milo is a twelve-year-old boy adopted from China who lives with his parents at Greenglass House, an inn catering to smugglers. He longs for a peaceful holiday and feels overwhelmed when a group of eccentric strangers suddenly arrives during a snowstorm. To cope with the chaos, he adopts the role-playing persona "Negret," a blackjack skilled at sneaking and finding hidden items. He harbors quiet questions about his birth family but fears upsetting his adoptive parents.

Meddy is the energetic younger daughter of the inn's chef. Finding the house full of secretive adults boring, she initiates a role-playing game called Odd Trails with Milo. She takes on the persona "Sirin," an invisible winged scholiast, and acts as the driving force behind their investigation into the guests' hidden motives.

Mr. Vinge is a tall, skinny man wearing large glasses who arrives as the first unexpected guest at Greenglass House. He is highly secretive about his occupation and motives for visiting the inn during a snowstorm. His missing pocket watch becomes one of the first mysteries Milo and Meddy attempt to solve.

Mrs. Hereward is an older woman with a hair-trigger temper who spends her time knitting and drinking tea. She carries a ditty bag adorned with a mysterious iron gate watermark. Despite her gruff exterior, she possesses a deep passion for history and shares Nagspeake fables that capture Milo's interest.

Owen is a young man adopted from China who braves a severe blizzard to track someone down at Greenglass House. He carries a dragon figurine as a good luck charm. His arrival profoundly affects Milo, offering him a rare connection to someone who shares his cultural background.

Ben Pine is Milo's adoptive father and the co-owner of Greenglass House. He is warm, supportive, and accustomed to the strange behaviors of the smugglers who frequent the inn. He once played the Odd Trails role-playing game as a boy and tries to remain patient despite the chaotic holiday rush.

Nora Pine is Milo's adoptive mother and the co-owner of the inn. She is practical, nurturing, and works tirelessly to accommodate the uninvited guests during what was supposed to be the slow season. She constantly checks in on Milo to ensure he is adjusting to the disruption.

Georgie is a young woman with distinctive blue hair who arrives alone at the inn. She brings a special pinhole camera called "Lansdegown" and kindly lends Milo a book of Nagspeake folklore. She maintains a quiet demeanor but displays a tense, hidden history with Clemence.

Clem is a highly athletic young woman with red hair who requests a room on the top floor purely for the exercise. She jokingly refers to herself as a cat burglar and displays an intense curiosity about the other guests, paying special attention to Georgie's activities.

Dr. Gowervine is a grumpy, serious guest who arrives alongside Mrs. Hereward. He carries a heavy satchel and claims to be visiting specifically to study the inn's famous stained-glass windows. He is easily irritated by the chaos of the unexpected gathering.

Mrs. Caraway is the dedicated chef at Greenglass House. She works closely with the Pine family and brings her daughters to help manage the kitchen when the inn suddenly fills with winter guests.

Lizzie is Mrs. Caraway's older daughter and a skilled baker. She assists her mother in the kitchen, working hard to keep the stranded guests fed and comfortable during the massive blizzard.

Fenster is a smuggler and regular at Greenglass House who seeks refuge from the cold. He is loyal to the Pine family and fiercely defends the reputation of historical smugglers against outside judgment.

Brandon is a conductor for the Nagspeake Belowground Transit System. He braves the frozen, dangerous conditions to safely deliver passengers to Greenglass House when the main routes become impassable.

Also known as Michael Witcher, Doc Holystone is a legendary Nagspeake smuggler whose history looms over the inn. Though a figure from the past, his history and the rumors of his hidden treasures dominate the guests' conversations and investigations.