All hope is lost when Ninjago City succumbs to the Overlord's third invasion. Masquerading as criminals, Nya and Skylor infiltrate the Overlord's ranks; intending to destroy the invader from within. But when a ghost uses the ensuing chaos to seize control, the girl's lives quickly become a dark game of 'Simon says'... where both the Overlord's forces and the Ninja want them dead.