Ever since she was young, Eva Ushiromiya has worked tirelessly to prove herself as the ideal successor to the Ushiromiya family headship. Despite facing endless discrimination as a woman, she is determined to overcome the odds and surpass her older brother Krauss, who is set to inherit the position by way of birthright.

An opportunity to realize her dream comes at the annual conference on the island of Rokkenjima. With the announcement of the epitaph's riddle, Eva believes that finding the hidden gold will force the rest of the family members to acknowledge her. However, as the adults of the Ushiromiya family decipher the puzzle, a string of unexplained murders ensues, forewarning the unfortunate fate that awaits them in the end.

Meanwhile, the game board between the Golden Witch Beatrice and Battler Ushiromiya commences once more—bringing new yet unlikely accomplices to participate in the duel.