'The Killer Is One of Thirteen' is the English title of the film and that basically is the plot. It's a Spanish giallo film. A widow invites twelve people to her remote house as she suspects one of them may be responsible for the death of her husband in a plane crash. Throughout the first hour of the film there is endless talk about motives and relationships and evidence. It is hard to keep up with who is who and what is what as there are so many people to keep tabs on. Then after an hour the grisly killings begin (by someone in black gloves naturally) to liven up the proceedings and the film rushes through to the weak conclusion where all is hurriedly explained. It had potential but did not live up to it.The characters were bland and the acting was too. The great Paul Naschy is in it but certainly not enough. He appears now and then almost randomly. As giallos go it is average.

This exciting film contains tension , thriller , drama , mystery , plot twists and shocks , including decent scares with tense killing sequences especially in its final part , in a creepy denouement . Slowly paced flick with a fairly suspenseful and horrifying story in which a killer series undergoes a killing spree by means of brutal executions . This thrilling picture concerns about some higher-class people are gathered by a widow , Lisa Mandel(Patty Shepard) , in an isolated mansion under mysterious circumstances and one by one they are murdered , each according to a peculiar relationship with Carlos Mandel , the formerly deceased husband by aviation crashing . The beautiful widow invites a number of guests to stay at her residence , these are the followings : Francis , widow's cousin (Eusebio Poncela) , his mother (Trini Alonso) , the playboy Harry Stephen (Simón Andreu) , Martin (José María Prada) and lover , Srta. Hoven (Dyanik Zurakowska) , the suspicious painter , Harlan (Jack Taylor) , Guillermo (Eduardo Calvo) , his wife Laura (Carmen Maura) , among others . Furthermore , there appears servants , gardener (Blaki) maid (Marisol Delgado) and butlers (Ramiro Oliveros , Paul Naschy) . Later on , the widow reveals that she knows that one of the group killed her husband and she is attempting to search for hubby's murderer . As he really didn't die by plane crash , but he deceased by a sleeping pill that caused the deadly accident when he was crossing the Mancha Canal . Before dying , the husband to withdraw money from the bank : 10.000 pounds , this cash is , day-present, missing . Soon they are being too murdered one by one . As they are being killed by cutting car brake line , slitting , garrotting , hanging , and stabbed in the chest . Meanwhile , at the mansion occurs the regular loving conflicts , including sexual scenes , as sex with butler , as sex with a maid , triangles , jealousy , and betrayals . As the guests are astonishing about the inexplicable deaths are happening . The premise is the following : who's the killer among the suspicious guests ? The plot is plain and simple , regarding a group of wealthy people are invited by a widow and shortly after , realizing that they are being murdered one by one . This Giallo contains suspense , thrills , chills , intrigue and plot twists . Aguirre designs a mediocre thriller , including some regularly staged murders plenty of startling visual content with blood and gore , though was submitted to limited censorship in Spain . This is a customary slasher in which mystery , tension , suspense appear threatening and lurking in every room , corridors and luxurious interior and exterior . The picture packs atmospheric blending of eerie thrills and creepy chills combined with a twisted finale . It displays lots of blood but it seems pretty mild compared to today's gore feasts . The staged killings are the high points of the movie , they deliver the goods plenty of screams , shocks and tension . This "The Killer Is One of Thirteen" contains usual ingredients of the ¨Gialli¨ sub-genre : suspenseful intrigue , twisted killings , violence , sadism , physical abuse , and some female nudity . Based on a script by Alberto Insua , soon after Javier Aguirre adapted the screenplay . The main excitement lies in watching what new and amazing killing to be committed by a strange executioner , a black gloved killer . Sensationalist murder pieces , including by axe in the head , killed in shower , stabbing , asphyxiate , head bashed in , decapitation and grisly slashing . However , the film results to be slow-moving and extremely talking , for more of a hour , there happens nothing . The Giallo plot is mingled with the typical Agatha Christie mystery developed in her known novel ¨Ten Little Indians¨ that had several cinematic adaptations , such as 1965 rendition by George Pollock , 1975 recounting by Peter Collinson and 1989 retelling by Alan Birkinshaw . The cast is pretty good , plenty of known Spanish actors , such as : the gigoló Simón Andreu , Eusebio Poncela , Alberto Fernández , May Heatherly , Paloma Cela , Jack Taylor , Dyanik Zurakowska , Eduardo Calvo, Jacinto Molina , Ramiro Oliveros and several others .The motion picture was regularly directed by Javier Aguirre and it has several flaws , gaps and failures . Javier Aguirre has filmed with all of the power and sensationalism at its command but in exploitation style . Father of director Arantxa Aguirre with first wife , actress Enriqueta Carballeira , being his second wife Esperanza Roy , both of whom usually play his films . Javier is a craftsman , expert on comedies such as : ¨El Astronauta¨, ¨Los Que Tocan El Piano¨ , ¨Locuras De Parchis¨ , ¨Los Chicos Con Las Chicas¨, ¨Soltero Y Padre En la Vida¨, ¨Soltera Y Madre En La Vida¨, ¨Rocky Carambola¨, ¨Martes Y Trece¨. Aguirre also made quite a few terror movies as ¨Gran Amor Conde Drácula¨, ¨Jorobado De La Morgue¨ , ¨Asesino Está En Sus Trece¨. In addition , he directed various ¨Avant Garde¨ films.

I used to be ecstatic and very hopeful every time I stumbled upon an obscure horror title that didn't yet have a single user-comment here on IMDb, but few years and several disillusions later, I'm now rather wary and skeptical whenever I'm the first person who has to submit a review. One of the many things I sadly learned over the years is this: if in this hi-tech day and age, with new media and advanced restoration techniques, a certain movie is still undiscovered, well then that's probably for very good reason! Or, in other words, it's probably a movie so bad that it deserves its status of total obscurity. "The Killer is one of Thirteen" is such a discovery that made me cautious… It's a giallo from Spain. This wondrous horror sub-genre, which happens to be my favorite stream of '70s exploitation cinema, originates from Italy but a handful of clever Spanish directors jumped on this profitable wagon as well. Spanish gialli generally are a lot less stylish and qualitative than their Italian counterparts, but still there exist a few worthwhile gialli titles from Spain, like for example "A Dragonfly for Each Corpse", "The Fourth Mrs. Anderson" or "Seven Murders for Scotland Yard". This "The Killer is one of Thirteen", on the other hand, is completely unknown, but let's give it an honest chance because – after all – it does benefit from a typically attractive giallo title and synopsis, and it stars the one and only Spanish horror monument Paul Naschy (albeit in a much smaller supportive role than usual) The plot resembles another umpteenth and shamelessly blatant imitation of Agatha Christie's "Ten Little Indians". Not ten but thirteen unsuspecting people are heading towards a secluded mansion in the country, following an invitation of the young and beautiful widow Lisa Mandel. There aren't any logical connections between them, except that the lady of the house is persuaded that every single one of them could very well be the potential murderer of her late husband. Via the element of surprise of this confrontation (and after ordering her staff to sabotage their cars so that they can't escape), Mrs. Mandel hopes to identify the real culprit. Rather than to confessions, the gathering leads towards painful revelations, double-crossing and – of course – vicious new murders! "The Killer is one of Thirteen" honestly isn't a disastrous effort, and I'm really glad I saw it, but director/co- writer Javier Aguirre nevertheless makes some fundamental rookie mistakes. First and foremost frustrating: for more than a full hour, there's nothing happening except talk, talk, talk and … more talk! Seriously, because of the overly talkative first hour, the body count is disappointingly low! When you put the number thirteen in your title and plot description, you basically imply that the body count will be ginormous and in that case you can't afford that more than half of your ensemble cast survives the ordeal! And another thing, the title and plot description are quite misleading. There are thirteen guests invited to the mansion, but there are also four members of the household staff that behave increasingly suspicious, so in fact the killer is one of seventeen. Never overlook the household staff; that's a mistake Agatha Christie didn't make. And yet, in spite of having so many suspects with so many versatile motives, the film foolishly reverts to literally the oldest cliché in whodunit-history when the moment arrives to reveal the killer's identity. But hey, there's also a fair portion of good stuff! Since the first hour is so bloodless and gossipy, Javier Aguirre has got oceans of time to introduce all characters in great details. They're a bunch of loathsome and selfish aristocrats, with only power, money or lust on their minds. The amount of murders may be bitter low, but the least you can say is that they are vile and nasty! The cast contains few familiar names, but the performances are quite adequate. Paul Naschy makes a small but remarkable appearance as the perverted chauffeur. In the release year of this film, 1973, Naschy starred in no less than nine horror movies. Apart from this one, two more of those were directed by Javier Aguirre: the much inferior "Count Dracula's Great Love" and the much superior "The Hunchback of the Morgue". Busy guys, those Spaniards