It is around one o'clock on the last Sunday in December. The body of an old man is found in the executive suite on the top floor of an office building in Roppongi, Tokyo. He has been beaten to death. The victim (who had been taking his customary after-lunch nap) is Shozo Ebara, president of a nursing company due to launch its IPO next spring. Since someone had recently been taking pot shots at Ebara's office with an air rifle, strict security measures were in place. Windows had been replaced with reinforced glass, the elevator could only be accessed with a security code, and cameras monitored all the building's passageways. No murder weapon is found, but the police arrest Hisanaga, the managing director who had been dozing in his office next door, as their prime suspect. Hisanaga, however, had been Ebara's friend and protégé for 40 years. Suspicion next falls on Ebara's adopted son-in-law Masaki. In his mid-thirties, Masaki is not only next in line for the top job but is due to inherit all his father-in-law's property. Was this a locked-room murder mystery, or simply an accident? At Hisanaga's request, Junko Aoto, his lawyer, teams up with Kei Enomoto, renowned security consultant, to unpick the mystery. They discover that the president, who had been given only a year to live after an operation on a brain tumor, and the managing director had teamed up to embezzle 600 million yen of the firm's money. As the Sherlock Holmes-like Enomoto sniffs out a range of possible explanations from detailed analysis of the crime scene, Aoto, the Watson figure, throws out a series of red-herring interpretations of her own. A mystery tour de force featuring brilliant displays of deduction, and culminating in an ingeniously crafted surprise ending.
The Enomoto-Aoto pairing proved so popular that two follow-ups have been released: Kitsunebi no ie (The Mirage House) and Kagi no kakatta heya (The Locked Room).