Despite not being credited as a writer, Smith made very significant changes in the second half of the script, including a new ending. All the scenes of Black Death were shot in chronological order, a rare occurrence.
The film takes place in 1348 in plague-ridden medieval England. Osmund (Redmayne), a young monk, has been separated from other people in order to see whether he shows any symptoms of having the plague. After he is released, he sneaks away to meet with a woman, Averill, whom he loves despite his vows of chastity to God as a result of being a monk. Osmund tells Averill the plague has reached the monastery and she must leave to escape the disease. Though Averill asks him to run away with her, he wants to stay at the monastery. She promises to wait for him for one week at a meeting place in the forest in case he changes his mind. Osmund prays to God asking for guidance on whether he can serve God outside of the monastery in order to join his lover Averill. At that moment knight Ulric (Bean) arrives with orders from the Bishop to take a monk as a guide on a quest into the forest. Osmund decides this is a sign from God and volunteers to go. After leaving, Osmund learns that Ulric and his group of mercenaries are tasked with finding a remote marshland village which has remained untouched by the Black Death. The town is said to sacrifice people in order to remain free of the plague, and they are rumored to be led by a necromancer who is able to bring the dead back to life. Their mission is to capture the necromancer, put a stop to the town's sacrifices, and bring the necromancer back to the Bishop. Osmund is supposed to guide them to the village because he has knowledge of the surrounding forest and marsh from his childhood.
On the way to the village, Osmund leaves the group while they are sleeping one morning in an attempt to meet with Averill at their meeting spot. Osmund finds Averill's horse and her torn blood-stained clothing in their meeting spot. He also sees a group of bandits and thieves nearby in the forest and runs back to Ulric and the mercenaries. The bandits from the forest attack Ulric, Osmund, and the mercenaries. Though the bandits are defeated, one member of the mercenary group is killed and Osmund is stabbed (not fatally, but badly). Eventually, Ulric and his group find the village they seek beyond the forest and marsh. The village is an eerie disease-free utopia led by a beautiful woman, Langiva (van Houten). Ulric's group initially claims to be seeking shelter (hiding their true purpose) because they are unsure who the necromancer in the village is and want to draw the necromancer out with deceit. Ulric does not trust the villagers. Ulric tells Osmund that an earlier group of four men had been sent by the church to find the village as well, none of the four men had returned, and Ulric found one of the group's church-medallions being worn by a villager who claimed to have found it in the marsh. Langiva treats Osmund's wound from the bandit attack and then leads Osmund to the body of Averill. Langiva claims that she had found Averill injured in the woods, and that Averill had spoken about Osmund just before her death. While treating Osmund's wounds Langiva reveals that her husband had been killed by "men of God". That night the town has a feast welcoming their guests. As everyone eats Langiva leads Osmund into the forest where many women are performing a ritual over the buried body of Averill. During this ritual Langiva appears to resurrect the dead body of Averill, and Osmund runs away upon seeing this. Osmund runs into the crucified corpses of the four men who had previously been sent by the church, and he is taken prisoner by the town. At the feast, Ulric and his mercenaries are drugged and then taken prisoner by the town. They all awake the next day tied in a pit of water.
Langiva and the villagers tell the prisoners they know the men had come to the village to do them harm, and they had found Ulric's torture machine which he had brought and hidden in the forest for the purpose of capturing and transporting the necromancer to the Bishop. They offer the men a choice of death or to renounce God and be allowed to leave the village. The first mercenary refuses to renounce God, he is crucified, and his stomach is split open. A second mercenary agrees to renounce God and is led away by the villagers while being told he will be freed at the edge of the village in the forest; in reality, once outside of the village they hang him by his neck from a tree until he is dead. Langiva then takes Osmund from the pit and says that she has brought Averill back to life, she says Osmund must renounce God, but then he will be allowed to live in the village with Averill for the rest of his life. She points him towards a hut where Averill is located. Osmund walks into the hut alone and finds Averill alive, but seeming to be possessed. She is drooling, she can not focus her eyes at all, she does not speak except gibberish, she does not react to or recognize his presence, and she is holding a knife which she stabs into a wooden table and into a wall. She even briefly seems to half-hardheartedly (though not vigorously) try to attack Osmund when he touches her. Osmund believes Averill is a zombie or possessed, or that her soul is trapped in purgatory, and he kills Averill in order to free her soul from purgatory and from the witch's spell so that Averill's soul may ascend to heaven. He carries Averill's dead body to the villagers, and Langiva says that the Christians are so cruel that they kill the ones they love. Osmund slashes at Langiva's face. The villagers stop Osmund and beat him bloody and near unconsciousness. During the beating, Osmund drops his knife next to the remaining prisoners. The villagers then take Ulric from the pit and tie his arms and legs to ropes attached to two horses pulling in opposite directions. Langiva attempts to make Ulric renounce God. Ulric calls for Osmund (who is permitted to approach), and Ulric orders Osmond to remove his shirt. When Osmund removes Ulric's shirt it is seen Ulric is infected with the plague and that he has thereby brought the plague into the uninfected village. The villagers then whip the horses so that they pull Ulric's body apart limb from limb.
At that moment the remaining two prisoners/mercenaries grab the knife Osmund had dropped earlier and free themselves. The two mercenaries are battle-tested and manage to kill all of the untrained villagers that oppose them, though one of the two mercenaries dies in the battle. The last remaining mercenary takes the village's second-in-command male as prisoner to be presented to the Bishop as the necromancer the group had been sent to find. During the final battle, Osmund chases Langiva into the marsh in an attempt to kill her. In the marsh, Osmund loses Langiva in the mist and fog, though they shout to each other through the fog. Langiva reveals that she is not a witch at all but simply a herbalist who is skilled with plants and drugs. She says that Averill had never been dead at all, Langiva had drugged Averill, and that Osmund killed her himself for the one and only time. Osmund asks why they had buried Averill if she had not really been dead, and Langiva says that it is because "people need miracles" and people worship the one who provides the miracles. Langiva had used drugs and fake ceremonies to make herself appear powerful in order to gain leadership over the village. She also did this to sway the villagers away from Christianity which Langiva believes is evil because it leads men to commit terrible acts in the name of God and religion. Osmund collapses from grief and shouts at Langiva to bring Averill back (seeming as if he does not believe or is unwilling to believe that Langiva has no powers). Langiva says that she can't bring Averill back and that Osmund should pray to his God for help. Langiva disappears into the mist and escapes. Osmund and the last surviving mercenary return to the monastery with the male "necromancer" villager in tow as their cargo.
In the final scenes, the last surviving mercenary acts as a narrator. He says the village had been untouched by the plague because it had been remote and far removed from other towns (and not because of the "witch's protection"). However, after the mercenaries brought the plague with them, the surviving people in the remote village and forest also fell victim to the plague. Finally he says that in the years that followed he heard stories that Osmund had lost his heart, had grown cruel, and took up the sword in God's name. Osmund was torn between the possibilities that he had killed his drugged lover Averill who had never been dead at all, versus the belief that she was a demon-possessed corpse resurrected by the witch Langiva, and at least in his behaviour, it appears he ultimately sides with the latter supernatural explanation. An older church-empowered Osmund sets out with soldiers to hunt and kill Langiva and other witches throughout England. The audience is shown scenes where Osmund appears to falsely mistake other women for Langiva, as well as falsely accuse many other women of witchcraft, all of whom are ultimately tortured and executed in the name of God.
Black Death was developed and produced by Douglas Rae and Robert Bernstein at London's Ecosse Films, with Phil Robertson of Zephyr Films acting as physical producer. Ultimately it could not get off the ground in the UK and became a 100% German production.The film was financed solely out of Germany, with Jens Meurer of Egoli Tossell Films acting as producer.
The film was originally due to be directed by Geoffrey Sax. Rupert Friend and Lena Headey were attached to star. Famke Janssen was later considered for Headey's role. After he was attached to direct Black Death, Smith suggested Carice van Houten, Tim McInnerny, and John Lynch for their respective roles.
The film was shot in the German federal state of Saxony-Anhalt at Blankenburg Castle in the city of Blankenburg and Castle Querfurt in Querfurt and Zehdenick, Brandenburg in the first half of 2009. Van Houten's first day on set was 14 May 2009. Technical elements included production design by John Frankish, a spartan score by composer Christian Henson, and cinematography by Sebastian Edschmid.
Smith explained his approach to the film:
It's a 'medieval guys on a mission' movie. The period of the black death – what's fantastical and rich about that period? I said, 'What if we took a realistic approach?' The people of the time believe the plague was sent by God to punish them for their sins, or by the Devil to torment them. I wanted to find out what the characters felt and posit them on a journey of 'is it real? Or is it not real?' What would a necromancer be like if he existed? We added this fundamentalist knight, so it touches on fundamentalism. It's a super dark film but it's exciting. It's like a dark parable about how things haven't really moved on in the last 600 years.
In the original script, the second half of the film turned to be entirely supernatural: Langiva was revealed to be the reincarnation of the Devil, while Osmund "was actually in Hell and Hell being in the physical place". Smith changed these elements to represent the idea that to him "Hell is the Hell you are in within yourself", as he tried to represent in Triangle. Because it was considered too dark, producers tried to cut Smith's ending from the shooting schedule. However they changed their minds two days before the shootings of the epilogue.
International sales were handled by HanWay Films. Amongst other deals, Revolver Entertainment/Sony acquired the rights for the UK and planned a release on 28 May 2010, while Wild Bunch distributed the film in Germany. The film is part of the Canadian Fantasia 2010.
Review aggregator Rotten Tomatoes provides links to 59 reviews of the film, 68% of which are positive. The critical consensus states: "Black Death delivers the fire and brimstone violence its subject matter warrants, while posing some interesting questions of faith and religion." In an advance review, Leslie Felperin of Variety wrote "A savvy, stylish horror-actioner that's more than the sum of its genre parts, Black Death manages to deliver enough suspense and bloodletting to appease gore fans... Use of grainy stock and a preference for special effects rather than visual or CGI effects gives it a pleasingly retro feel, as does its willingness to explore uncomfortable moral ambiguities. Tech credits create a strong, fetid atmosphere on what looks like a low budget. German locations in Saxony look appropriately beautiful, sinister and ancient all at the same time."
Alan Jones from Film4's FrightFest concluded: "Some may find the climax rather disconcerting as Smith pulls the rug from under one’s feet. However, the greater percentage will thrill to the way the eerie and puzzling intensity builds up a compelling head of scream as the stark brand of Witchfinder General shock value rears its head in the most startling of codas. This intelligent original represents a commendable break from the genre norm and is one of the most powerful films made about God, the godless and what the Devil truly represents."