Meliodas and Hawk stumble through a portal above the clouds into the Sky Palace, home to the Celestials, winged descendants of the Goddess Race who guard an ancient demon sealed since the end of the Holy War three thousand years ago. When the Six Knights of Black, a Demon Clan strike force, arrive to break the seal and unleash the beast, the rest of the Seven Deadly Sins follow Meliodas skyward to stop them.