With the help of her white friend Marie-Grace, Cecile, a well-to-do black girl in 1853 New Orleans, plans a secret adventure at a Mardi Gras costume ball.

When Marie-Grace arrives in New Orleans in 1853, she is not sure she fits in, until an unexpected invitation opens the door to friendship.

"Marie-Grace can't wait to begin her journey up the Mississippi River with her father. The steamboat they're traveling on is the biggest and fanciest boat Marie-Grace has ever seen. It's crowded with all sorts of interesting passengers, including Wilhelmina Newman, a girl her age. Wilhelmina is traveling alone, and she's carrying a secret in one of her trunks--clues to hidden Gold Rush treasure. Marie-Grace and Wilhelmina have to unravel the clues...

Eleven-year-old Cécile Rey searches through many corners of 1854 New Orleans seeking a necklace, borrowed from her Tante Tay, that disappeared as she was exiting a crowded showboat. Includes facts about the 1850s.

Encouraged by her friend Marie-Grace, Cecile finds a way to help her beloved city, New Orleans, in the aftermath of the 1853 yellow fever epidemic.