Mad and Rik, an orphaned pair of twins living together in Europe, receive a digital summons to try to hack a mysterious offshore bank. Rik revels in the idea of meeting this intense challenge, while Mad believes that they should continue to stay on the run so as to avoid detection by the Syndicate.
The siblings experience conflict with eachother for the first time in their lives as Rik seeks to achieve glory for himself by doing the impossible. He and Mad remain tense as they travel to the Bank of Usher on the Isle of Sky, knowing that they face increased danger due to their weakened sense of teamwork. Mad deeply wants to stop undergoing so much risk and move somewhere safe where she can get her GED.
The siblings enter the bank and meet Dr. Tarn, who oversees the security recertification attempts and partly consists of artificial intelligence. He lets the twins know that they have twenty-four hours to complete their task. Mad explores with a drone and learns that the mold growing on the house is partly sentient. When Rik disappears, she goes looking for him and realizes that the bank does not contain any physical money but seems to function as a crypt. She uses the mold as a tool to her advantage and it destroys the bank. Later, she and Rik wake up at a local hospital, where Mad is asked to join a government hacking agency.