Mangled limbs have been turning up all over Ninjago city and the people are scared. Ten murders in ten weeks, all committed with a sword, and still nobody has a clue who the mysterious killer is. Green Ninja and volunteer Ninjago City Defence Department worker Lloyd Garmadon doesn't know it yet but he is the only one who can stop the killer. When Nya is kidnapped on a mission, Lloyd finds himself thrown into the centre of the investigation. His only clue is a cloth with the initials A.S. He enlists the help of his best friend, Nya's brother, Kai Smith. Can the Fire Ninja help Lloyd find the answers before the deadly killer strikes again.