Zhang Chulan and Feng Baobao take on a special assignment from their employer: escort a legendary sword called Hiruchiwan to the border, honoring an agreement made decades ago with Japan's Ishikawa family. Along the way they must cooperate with teammates they barely know and endure a bitter northern winter. Powerful foes known as the Bihe Ninjas want the blade for themselves, and the struggle to protect it plays out across snowy fields and forests.