Portuguese mystery fiction began in the mid-1800 under heavy influence, not of Poe, but of the French social-crime novels of Eugène Sue and his followers. It's not a particularly interesting phase from a GAD point of view. Camilo Castelo Branco, an early follower of Sue, later became one of the two major Portuguese 19th Century novelists, and his books often feature mysterious crimes and their solutions; there are some literary masterpieces here, but they are not detective stories.
By the last three decades of the 18th century, Poe's mystery novels and Gaboriau's feuilletons were widely read. There are some good crime/mystery novels and stories from this period, but nothing exceptional. The Portuguese tend to be on the cynical side: the first true detective stories that appeared in this period were already critical deconstructions and parodies of the Detective Story. A major spoof: in 1870, one of the main daily newspapers published a series of letters to the editor containing a supposedly real-time account of a mysterious murder occurred in the surroundings of Lisbon and of the subsequent events; the tale was believed as true by the public, quadruplicating the sales of the newspaper, and the police actually investigated the matter. The last letter revealed the whole story to be a (not unworthy) mystery novel by J. M. Eça de Queiroz (the other major 19th Century Portuguese novelist) and his friend mainstream writer Ramalho Ortigão (a Gaboriau fan). This kind of literary joke almost destroyed the Portuguese detective story in its berth, but ultimately also paved the way for more serious stuff.
Inevitably Sherlock Holmes triggered a string of imitators. Some of these are worthwhile: Maria O'Neill's Viscount Silvestre's and Rocha Martins' Chief Jacob's are the best detective stories of this era (both O'Neill and Martins were respected mainstream writers). One of the earliest books of Sherlockian apocrypha (with some good stories in it) was published in 1911 by Gustaf Bergström, a Portuguese undergraduate of Swedish descent.
Portuguese GAD books of the 20's and 30's are mainly imitative of second or third grade French, British and American authors. Most of these books are uninteresting; some are acceptable if compared to standards previous to the then ongoing British, American an French GAD. An exception is Reynaldo Ferreira, a wildly imaginative journalist/pulp writer that, while prone to writing total rubbish, was also capable of producing gems of GAD plotting, among them several impossible crime and armchair detective stories. Even his best stories are highly unconventional and like nothing else I know of: maybe a mixture of Doyle, Wallace, Harry Stephen Keeler and pure GAD authors (which he seemed not to have read much, by the way).
The systematic translation and critical appraisal of first grade GAD writers began only in the thirties, so the Portuguese true GAD also begun late. Fernando Luso Soares also published some interesting but thinly plotted fair-play detective novels. The same applies to most of the work by Artur Varatojo. The first major Portuguese pure GAD writer was José da Natividade Gaspar, who wrote a dozen interesting to good GAD novels and several short-stories (virtually unknown today) from the 30's to the 50's; some (not the better ones, I'm afraid) were translated in Spain and France.
The other main GAD novelist of this period was "James A. Marcus", a pseudonym of two cousins with diabolical legal minds, who wrote what I would single out as the only Portuguese GAD masterpiece novel, White Murder (that was the fake original title they gave for the book, anyway), published in 1950. This book features a donnish Oxford detective, an English country house setting, an amazingly cunning plot and a 50+ page, Ellery Queen-like, explanation of the crime that is one of the most compelling and convincing pieces of detective reasoning I have ever read. It would pass for an excellent GAD British mystery book of the kind (it even includes puns that only work in English and that were supposed to have been flatly "translated"). "Marcus" also published a very good collection of short-stories and three more novels, none as good as the first one. Two of these were written around this time but published only in the 80's and 90's. In fact, until this time, almost everybody thought that Marcus was an unknown British writer.
At the same time, a kind of Nationalist Reaction (in a literary, not political, sense) was taking place: authors like Victor Palla (a major architect and photographer) and Francisco A. Branco were urging others to abandon Anglo-Saxon pseudonyms and foreign settings in favour of a truly Portuguese GAD-style writing (they made the serious mistake of shunning "Marcus" from their circle). Both Palla and Branco wrote very good pure GAD detective short-stories; Branco also co-wrote a novel. Both published in EQMM, Palla receiving a honourable mention in the 1947 contest and Branco in 1950 (I would have to check the exact dates), earning high praises from Fred Dannay. Palla's story was even selected for at least one EQ anthology. In particular, Branco had a wild imagination. One of his stories deals with the murder of Snow White and the suspects are... well, you guess (but you wouldn't guess the culprit). This is a real tour-de-force: a pure fair-play fairy tale mystery story. In another story, the mystery is solved by Santa Claus, who stumbles on a corpse when coming down the chimney; this is also a fair-play story and, like the Snow White stuff, the Santa Claus part is not just fireworks - only Santa could have solved that murder! His EQMM story has a terribly politically incorrect title ("The Dwarves' Club"), but has an excellent plot, and the titular small persons are not stereotypes but real human beings (there is also a reference to a Jewish financier - but, fortunately, as being a very generous person!). I know for sure that Anthony Boucher translated many other Branco short-stories and they must be published in English anywhere, but I haven't yet managed to discover where. Meanwhile Palla became a mastermind mystery-book editor and guru and also edited two monthly mystery magazines (one of them with Branco), in which he tried to incentive portuguese GAD writing with moderate success. There are several good stories from this period, many of them one-offs, but few novels.
From the late 50's the octogenarian pseudonymous W. Strong-Ross published more than a dozen novels in which a genius detective battles mad scientists, criminal masterminds and serial killers; these stories seem to have been written 50 years before (and probably were), are often gory on the verge of bad taste, but have a certain period charm, are well plotted and are frequently fair-play (in France he would be a cult author). The last of the GAD Portuguese writers may be the pseudonymous "Dick Haskins", who from 1958 to this day has penned more than 20 books. These are weird GAD/soft boiled crossovers, some of them with very clever ideas but mostly with sloppy plotting. Foreign GAD authors continued to be very popular until the late 80's but by the end of the 50's Portuguese GAD writers were being replaced by pseudo-thoughs, pseudo-psychologists and pseudo-mainstream novelists.
Ana Teresa Pereira is a contemporary writer fascinated with GAD (in almost every of her books one finds references to Sherlock Holmes, Ellery Queen, John Dickson Carr and others, she has edited a Sherlock Holmes anthology, and one of her books is actually dedicated to Dr. Gideon Fell!), but she is mostly a post-modern gothic writer with crime and mystery elements and not a true GAD writer (I love her books, though).
Henrique Valle