The third lady

It all begins with a chance meeting in France between two Japanese people. One is Kohei Daigo, who works as a researcher and has discovered that a certain product that seems to cause cancer that was sent to his lab passed as being safe. Daigo knows, however, that his boss is in bed with the manufacturers & that the lab results are false. The other person is a woman, Fumiko Samejima, who starts talking to Daigo while the two of them are alone together in a small salon in a Paris hotel during a storm which knocked out all of the electricity. It is dark, they cannot see each other, and choose to sit back to back and share secrets. She wants a certain person to die, while he wants his boss to die because of his part in causing several young children to die of cancer. The brief interlude is over quickly and they both go back to their normal lives. Imagine Daigo's surprise when his boss turns up dead. Now he is faced with a dilemma...is the mystery woman the murderer, and if so, does he now owe her?