Berry and Hack are somehow able to escape from the Hyperverse that Phantom Zero pulled them into. But before long, Hack is apprehended by the customer center, who are investigating the Zero Phenomenon. The next day, Berry wakes up on the veranda of her apartment, and after trying to explain what happened, her friends point out to her that there is no evidence of Zero Phenomenon having occurred, much less of the kid she encountered. Not taking no for an answer, Berry decides to dig up proof behind the Zero Phenomenon.

Hack is being held at the customer center under suspicion of being Phantom Zero, where she's questioned about the crime of forcibly erasing Love. Meanwhile, Berry learns from the mysterious Finn about how he and his comrades are ghosts, citizens who live in the city despite not being registered. Finn is skeptical that a fellow ghost would have helped Berry, and obtains the data on Phantom Zero from the paper plane device of Hack's that Berry brought.

When Finn was young, his family lived in a slum where garbage tended to be dumped. One day, his brother brings him an older model of Deco that should be easier for Finn to use due to his Deco-Sickness. With it, Finn accidentally discovers that the local purification systems are broken. Believing this is what has caused his home to become polluted, he uses the Deco that he got from his brother to request that the customer center fix the purification system. But because he isn't registered as a citizen, his login is flagged as illegal, which leads to his request not being answered.

Thanks to Doron and his drone friends, Berry, Hack, and Finn are able to reach Mark Twain, a strange facility floating in the sky. By using the Angelfish club card they had previously obtained, they manage to get inside, where Berry and Hack enter Mark Twain's rendition of the Hyperverse. What they discover appears to be a labyrinth. Knowing that all the secrets of Tom Sawyer island must be contained within, Berry and Hack start searching for Phantom Zero's identity.