Oliver joins his sister Thea to find answers about Mar Novu's true goals. Diggle and Lyla go on a rescue mission, and in 2040, Mia and her team go up against the Deathstrokes.

Oliver, Laurel, Mia, and William travel to Russia to get the plans for a weapon capable of stopping the monitor, and Oliver faces reminders of his past with the Bratva. Meanwhile, Diggle recruits an ally to help him steal the plutonium for the weapon.