For most of us the notion of life in a tight-knit village is pure fantasy: We have lived our whole lives in and around cities. One would think, therefore, that we would have grown comfortable with the anonymity and the promiscuous mixing with strangers that define city life. Novels such as Hisaki Matsuura’s “Triangle” suggest, however, that cities, particularly those as multifarious as Tokyo, still make even seasoned urbanites nervous. Rich with possibility, cities are also rich with peril: They are places where anything can happen.