The Night Tiger by Yangsze Choo
Quick-witted, ambitious Ji Lin is stuck as an apprentice dressmaker, moonlighting as a dancehall girl to help pay off her mother's Mahjong debts. But when one of her dance partners accidentally leaves behind a gruesome souvenir, Ji Lin plunges into a dark adventure: a mirror world of secrets and superstitions.
Eleven-year-old houseboy Ren is also on a mission, racing to fulfill his former master's dying wish: that Ren find the man's finger, lost years ago in an accident, and bury it with his body. Ren has 49 days to do so, or his master's soul will wander the earth forever.