Shinji Wakatsuki is an insurance claims adjuster in the Kyoto office of Showa Seimei, one of the country’s largest life insurance companies. When he visits the home of policyholder Shigenori Komoda, 45, in response to a complaint, he finds Shigenori’s 11-year-old stepson Kazuya dead by hanging. Shigenori subsequently files a claim, and begins visiting Wakatsuki’s office repeatedly to press for payment. Because he knows Shigenori has received a fraudulent payout in the past, Wakatsuki suspects that he murdered his stepson in order to get the insurance money. A criminal psychology expert he meets through his girlfriend Megumi Kurosawa, who is studying psychology in grad school, tells him that Shigenori suffers from affectionless psychopathy and may well attempt to kill him.
The alibi Shigenori gives for the time of Kazuya’s death is subsequently confirmed, and the insurance payout is approved. Wakatsuki remains unconvinced, however, and continues to investigate the Komoda family on his own. Disquieting events begin to happen, such as silent phone calls and the killing of Megumi’s cat, and then the criminal psychologist is brutally murdered. Following this, Shigenori loses both arms in an accident and demands compensation under his accidental death and dismemberment policy. When Wakatsuki encounters Shigenori’s wife, Sachiko, in Shigenori’s hospital room, her suspicious behavior makes him realize that she is the mastermind behind the insurance fraud. Wakatsuki moves to void the insurance contract with the help of specialist Shigeru Miyoshi. Several days later, Wakatsuki returns home to discover that Sachiko has entered while he was away. Since Megumi is the only other person with a key, he realizes she must be in danger and hurries to the Komoda home. He finds Miyoshi dead, but is able to rescue Megumi.
Alerted by Wakatsuki, the police arrive, and Sachiko flees. More than a dozen bodies are dug up beneath the floor of the Komoda home?the Black House of the title?revealing the extent of Sachiko’s ruthlessness. With this, the case appears to be closed, but a colleague’s request that keeps Wakatsuki at the office late turns out to be a trap set by Sachiko, who is hiding in the building waiting for her opportunity to kill him. The two engage in a ferocious fight, in which Wakatsuki ultimately gains the upper hand and sends Sachiko to her death.
Weaving a story of horror and suspense that reflects real-life cases of insurance fraud, the author gives us a spine-tingling glimpse of the evil that can lurk in the human heart.