Commissario Trotti investigates crime in a small, unnamed city on the river Po in the north of Italy (sometimes erroneously identified as Padua). Trotti's career spans much of the First Republic, from the period known as the Italian Miracle through the Anni di Piombo. This milieu keeps the Polizia di Stato busy and in his enquiries Trotti frequently confronts problems facing Italian society: terrorism, political instability, corruption, socialism under Craxi, Operation Clean Hands (mani pulite), and above all, the decline of civilised intercourse.

Writing in a minimalist style, in which he relies largely on dialogue to advance the plot, Williams has at times been considered a demanding author. One critic complained that the books read like translations from Italian. Some readers find that pace and tension are sacrificed for sociology and politics and that the moody, brooding Trotti, addicted to rhubarb sweets, is too slow and too wordy for their taste.

The novels are populated with an array of acquaintances, colleagues, criminals, and the occasional walk-on, which together present a spectrum of the Italian national character. The author often uses minor characters to demonstrate the Italian penchant for labyrinthine and sometimes obfuscatory dialogue.

Having grown up under Fascism and having lost a brother in the partisan war of 1943-45, Piero Trotti is cynical yet dourly optimistic. By the fifth novel this optimism is in scant evidence. Trotti's estranged wife lives in America. A number of women find Trotti appealing but Trotti is torn in his loyalty to the marriage.

The primary characters, Trotti and the two subalterns with whom he works, employ a more restrained, direct discourse. Trotti himself is not expressive and seems impervious to personal relationships, but both lieutenants form close bonds with their demanding mentor. Magagna eventually leaves for Milan, in part to escape Trotti’s overwhelming influence. Pisanelli, who replaces Magagna as Trotti’s foil, is unable to remove himself from Trotti’s orbit and comes to both admire and resent his superior.

In the early novels Trotti's daughter Pioppi suffers from anorexia, a fact which continues to haunt Trotti for years, long after her recovery, and causes him to question his role as a father. In the later novels, Trotti is a grandfather to two little girls who give meaning to his life.