The most important holiday in NINJAGO is approaching: the Day of Remembrance. On this day, the residents of NINJAGO honor their ancestors and what they owe to them. For the preparations, the Ninja are invited by Dr. Saunders. They get to preview his exquisite collection, which includes dolls of the Ninja's former adversaries. During this, Cole accidentally discovers a magical blade filled with dark magic - the Yin Blade. This blade releases the spirits of the worst criminals who have ever lived in NINJAGO! At the same time, the blade traps Cole in the temple. Now it is up to the remaining Ninja to recapture the spirits and return them to the realm of memories before they gain the power to stay in Ninjago forever.