It has been understood for many years that, in order to have popular detective fiction, it needed to be written in a free, democratic society, which explains why virtually all the world’s principal detective stories were written by English or American authors. It is only in very recent years that the predominance of crime fiction being written mainly in English has changed.

There are, of course, exceptions, notably in 19th-century France, in which Emile Gaboriau and Fortune du Boisgoby enjoyed enormous success, as did Gaston Leroux after the turn of that century. Gaboriau’s famous policeman, Lecoq, was famous enough to be insulted by Sherlock Holmes, and the prolific du Boisgoby’s novels were reprinted so frequently that early editions may still be found in the bookstalls of Paris. Both writers were also translated and published in America and the United Kingdom. Leroux, most famous for having written “The Phantom of the Opera,” is often credited (erroneously, but still . . . ) with the first “locked room” or “impossible” crime novel, “The Mystery of the Yellow Room,” in 1908.

One would have to search long and hard to find detective novels written by Russians, Germans, Spaniards, Japanese, Italians, or natives of just about any other country, at least until very recent years. The reason is not elusive. In free societies, the police and their surrogates (private detectives, lawyers, etc.) represent law and order, organized to protect individuals from criminals. In repressive regimes, their primary assignment is to enforce government rule. They are more frightening to ordinary citizens than the most violent thugs or devious villains. Read any good mysteries from Islamic countries lately?

The notion of reading novels in which the police wear the white hats, where they are really there to help, has been so alien to the residents of most countries that it simply could not have existed.

This has changed since the end of World War II: Fascism was largely wiped out, Japan became a democratic state, and, eventually, the Berlin Wall came down and the Soviet states got a taste of freedom. Now, mystery writers flourish in Japan, Italy, Russia, and Spain, where Arturo Perez-Reverte has produced some exquisite books.

Robert Wilson is English, a graduate of Oxford University, but has set his novels in places that have not produced much in the way of local mystery writers. His earliest books were set in Africa (Ivory Coast, Nigeria, etc.). He then set one in Portugal, the brilliant “A Small Death in Lisbon,” which won the British Crime Writers’ Association Gold Dagger for Best Novel of 1999.

In 2003, “The Blind Man of Seville” introduced police Inspector Jefe Javier Falcon, who is also the central figure in his new novel, “The Hidden Assassins” (Harcourt, 464 pages, $25.00). Although not written by a Spaniard, Falcon is a milestone figure. The primary police force in Spain under the Franco regime, was the Garda Civil, which gave little attention to the niceties of law enforcement. It was regarded as an evil entity, a powerful force that could bring no good and no help to anyone in trouble. The Garda generally was the trouble, hence there could be no tradition of police detectives being heroic figures in Spain.

As with the previous two novels that feature Falcon, “Blind Man” and “The Vanished Hands”(2005), the beginning of “The Hidden Assassins” has all the appearances of what will be a police procedural, but it soon grows into something much larger.

During the course of a homicide investigation in “The Blind Man of Seville,”Inspector Falcon discovers his father’s journals and, in their pages, his participation in the Spanish Civil War and the atrocities he committed. Dealing with this knowledge, and the stress of his recently failed marriage, the novel turns into more of a character profile of the troubled policeman than a pure cop novel.

The sequel, “The Vanished Hands,” is a challenging study of a moral policeman who tries to find the links behind an apparent murder-suicide that includes the Russian mafia, a prostitution ring, the CIA, the events of September 11th 2001, the suicides of a famous actor and of a high-ranking policeman in Seville, and more. It’s enough to make your head hurt, but the stylish writing and the company of the hero make it worthwhile.

Now, in “The Hidden Assassins,” Mr. Wilson has produced another complex but beautifully written book. The discovery of a badly mutilated nude body (well, of course it’s badly mutilated; as opposed to what — nicely mutilated?) is the jumping off point to a police novel that quickly becomes bigger than a single corpse when an explosion blows up an apartment building, the mosque in its basement, and a nearby day care center, killing several Muslims, five children in the center, and the mother of one those innocent victims.

As Falcon investigates to learn if the mosque was the target of the attack, or if a bomb-making attempt went wrong, the plot becomes even darker and more elusive. Even the sensitive and intelligent policeman, the highest ranking in Seville, cannot provide all the answers.

While “The Hidden Assassins” is completely satisfying, with subplots involving Falcon’s own intricate personal life proving to be just as compelling as the political and criminal elements of the story, be prepared: Not every loose end is neatly tied up. As in the real world, that’s much too much to expect.

It is not an oversight. This outstanding author is meticulous, quite deliberately failing to allow his readers to follow some roads to their ends. There will be at least one more, probably two, adventures involving Falcon.

I, for one, look forward to traveling on those roads in his company.

Mr. Penzler is the proprietor of the Mysterious Bookshop in Manhattan and the series editor of the annual “Best American Mystery Stories.” He can be reached at ottopenzler@mysteriousbookshop.com.