Grace makes an unexpected visit to ancient Rome, a strange woman telling her to a find a lost scepter. Clara Voyant moves to Centerburg, telling Max she's having ghost troubles. A reclusive old actor reveals he has lived on many worlds, warning Max and Grace of a deadly alien horobotite invasion. In other words, just another day in the life of the amazing comet kids! In a desperate race to stop the horobotites, Max, Grace, Sophie, and the newest comet kid, Naomi, wormhole to the terrifying world of Erebus, confronting blue zombies, crimson serpents, white flies, and an unhinged robotic parking valet as they search for the elusive lost Scepter of Janus.