Who is Dark Night?

After the final battle between Batman and Batman Who Laughs, the Source Wall is destroyed. This has terrible consequences: Perpetua escapes from her prison. The Justice League narrowly survived the battle against Perpetua. You are being sent in search of something very important by the quintessence. Meanwhile, Tempus Fuginaut works several earths and recruits Wally West. With his help, he manages to gain access to Metron's Mobius chair and restores the balance between light and dark in the multiverse.