In 1919 Boston, an orphaned eighth-grade girl plans to head west to become a cowboy until the giant tank of molasses in her neighborhood explodes. Leah dreams of leaving behind the crowded streets of Boston's North End neighborhood to journey west. It's the only way she'll have the future she wants - one that doesn't involve her getting married or working in a factory. But then the molasses tank at the local plant explodes, sweeping through the city...