Spenser of Thin Air can be fairly easily related to the character appearing in the previous Parker books. He also can be compared to such series as those of Michael Z. Lewin's featuring Albert Sampson or Ed McBain's Matthew Hope books, both of which contain a flawed, often very human protagonist of the soft-boiled type. William Tapply and George V. Higgins have mined the Boston environment and helped to establish a real tradition of crime fiction set in the area. But the Spenser of the novels has evolved in quite different ways, and his on and off relationship with Susan is quite unique in both the prominence it receives in the books and in the importance it has on the developing character of the detective.