: A well-known professor is looking for the source of the plague bred by a geneticist. The plague is a virus of infertility, which should stop the overpopulation of the planet and save civilization from death.
In the prologue of the novel, a man escapes from his pursuers and throws himself from the highest tower of Florence. Before death, he thinks about his gift to humanity - Inferno.
Let the world remember me not as a monstrous sinner, but as a glorious savior ... Let humanity understand the meaning of the gift that I leave him.
Professor of cultural history, a specialist in symbols Robert Langdon comes to life in an unfamiliar clinic. According to the outlines of the buildings outside the dark window, he realizes that he found himself in Florence, although his last recollections are about Harvard University. With the help of a doctor, Siena Brooks, he finds out that the last two days have evaporated from his memory. According to Siena, amnesia is associated with a head injury and will pass soon.
A woman - an agent of a secret organization, the Consortium, is approaching the clinic. She was sent to deal with Langdon. The agent bursts into the chamber, but Siena has already led Langdon through the emergency exit. The agent shoots, but Langdon and Siena manage to leave in a taxi.
The Consortium chief is awaiting news. His organization arranges various falsifications, forms a false public opinion and hides clients from the law. This time, the boss contacted the wrong client, which is why the Consortium faces destruction. However, the client, recently dropped from the Florentine tower, left clear instructions that the chief intends to comply with. One of the instructions is to send a strange video on large TV channels on the appointed day, where a masked man talks about Inferno and pick up a bone cylinder from a bank cell. However, the cylinder is stolen, and the chief sends the agent to correct the situation.
Siena brings the professor to her home. Langdon finds in Siena’s apartment newspaper-cut articles about the child prodigy. Obviously this girl is Siena. The girl shows Langdon a biocapsule for the transport of dangerous substances, which was sewn up under the lining of his jacket. The capsule lock unlocks the fingerprint of Langdon. The professor calls the American consulate, and soon Siena sees a woman agent through the window. Langdon decides that the US government wants to kill him. For what? The answer may be in the container, and the professor opens it. Inside - a cylinder made of carved bone, which turned out to be a mini-projector. He projects a picture of Botticelli's Map of Hell, which illustrates part of Dante's Divine Comedy.
The professor notices that the picture is changed, and an inscription appeared on it:
Truth can only be seen through the eyes of death.
An armored car drives up to Siena's house, and people in uniform begin to search for Langdon. These are Supervision and Response Support (NDP) staff, and they are also looking for Langdon. Siena again saves the professor, who likes her more and more.
A female agent stalking Langdon from the roof of a nearby building discovers that the Consortium has removed her from work. Frightened, she decides to rehabilitate herself - to complete her task.
Since the mystery in the picture is connected with Dante, Langdon decides to go to the Old Town of Florence, where the poet was born and raised. The agent follows them. Langdon and Siena discover that there are police pickets at the gates of the Old Town - apparently the police are looking for them. They hide in huge gardens founded by the Medici. While they are trying to find them using a radio-controlled helicopter with a camera, Langdon guesses what is encrypted on the projection of the picture. The tip indicates the fresco, and the museum where it is exhibited is located in the Old Town.
Director of the World Health Organization (WHO) epidemiologist Elizabeth Sinsky recalls his meeting with a brilliant geneticist. He predicted that overpopulation of the planet would lead to the death of mankind, and believed that the “human herd” should be thinned out with the help of a plague epidemic. Sinsky understands that humanity will very soon exhaust the resources of the planet, but cannot agree with the methods that the scientist offers. However, he is sure:
Death is followed by birth. To reach Paradise, man must go through Hell.
Langdon and Siena are surrounded by police. They are selected from the trap thanks to the erudition of a professor who knows the architectural features of the Italian palaces of the Medici period. They fail to deceive the Consortium agent - a woman follows them on the heels. Langdon gets to the fresco, where the museum ranger recognizes him. She claims that the professor was here yesterday with her friend, the Italian art historian Busoni, they were considering the death mask of Dante. Langdon understands what the phrase means on the projection of the picture.
When Langdon asks to show him the mask, it turns out that she was stolen. The surveillance camera filmed as Langdon and Busoni steal a death mask. From the caretaker, Langdon learns that the mask is the property of billionaire scientist Bertrand Zobrist. Siena is aware of his theory of demographic apocalypse. The caretaker calls the police. Langdon does not remember where the mask is, and cannot return it. The caretaker calls Busoni's secretary and finds out that he died of a heart attack the night before. Before his death, he left a message:
What you are looking for is securely hidden. The gates are open for you, but you hurry. "Paradise," Twenty-fifth.
This is a hint at the last part of Dante’s Divine Comedy. The museum is surrounded by Bruder's people, but Langdon and Siena again escape the trap and set off in search of a mask. The agent follows them and dies.
On the way, Siena tells Langdon about the Zobrist and his desire to use genetics not to heal, but to destroy people. After meeting with Sinsky, the scientist became an outcast and hid until he died, dropping from the Florentine tower. Siena believes the Zobrist is right.
Busoni's tip leads Langdon to the old city baptismal center, where he also received the baptism of Dante. They are followed by a person with a face covered with a rash. They distract the attention of the guard, penetrate the baptismal room, the main gate of which is not locked, and find a mask. Its inside is covered with a primer for canvas. Having cleared it, Langdon discovers poems that mention the treacherous doge, the museum of sacred wisdom and the underground palace.
In the Langdon baptismal hall, Siena overtakes a man with a rash on his face. He is introduced by Jonathan Ferris, WHO staff member, and states that the professor works for them. Siena is inclined to trust him, but Langdon does not remember anything. The verse on the mask leads to Venice, where they all go together, after having previously knocked the Poland’s detachment off the trail.
In a separate compartment of a high-speed train, Ferris says that Sinsky attracted a professor to unravel the mystery and showed a bone cylinder that she had removed from Zobrist’s bank cell. Now Langdon realizes that he is looking for the source of the plague, and the fate of mankind depends on his ingenuity.
The Consortium Chief changes his rules and views the video left by the Zobrist. What he sees scares him, and the chief calls the FS-2080 agent, who is located next to Langdon. It was FS-2080, associated with the Zobrist, who recommended him to turn to the Consortium. For a whole year the organization hid a scientist from WHO, and he created his own virus. The chef contacts Sinsky.
FS-2080 thinks of a deceased lover who was not only a lover, but also a teacher. He believed that evolution should be artificially accelerated. The agent wants to finish his business.
In Venice, it turns out that Langdon was mistaken, the doge’s museum and grave are in Istanbul. Chef, Sinsky and Bruder also fly to Venice.Langdon does not know that the NDP is one of the units of the World Health Organization. He again tries to escape from Bruder, but only Siena manages to escape.
Langdon is dating Sinsky and the boss. They show him a video of Zobrist, where a bag of dissolving plastic is lowered into the water. When the bag bursts, its contents will fall into the water and infect it. Langdon learns that Siena was Zobrist's mistress and agent for the Consortium. Siena, being a child prodigy, could not find her place in life. She wanted to save the world, but she understood how to do it only when she met Zobrist. Starting to hide from WHO, the scientist threw Siena, she resorted to the help of the Consortium, but found him too late. She saw her beloved commit suicide.
Langdon's brain injury is a fiction. The Consortium staff with the help of drugs provoked amnesia in Langdon and put false memories. All this was done so that Lagdon began to trust Siena and return the projector. Siena used his knowledge to find the source of the plague first. Langdon Siena likes, he can’t recover.
By plane WHO Langdon flies to Istanbul. On the plane, he sees Ferris, who also turns out to be an employee of the Consortium. In Istanbul, they find an underground hall with a lake, which turned out to be an ancient city reservoir, where tourists are now allowed. The reckless Siena follows them.
Langdon’s efforts are in vain: the bag is dissolved, infection has occurred. Seeing Siena in the underground hall, Langdon chases after her. She can run away, but she remains - she has nowhere to run. Siena tells Langdon about the letter of the Zobrist, which she received before the disappearance of the scientist. Zobrist wrote to her about the virus he invented, which invades the human genetic code and causes infertility. He loved humanity. Not wanting to kill millions of people, he came up with a safe alternative to the plague.
There will be no hospitals overflowing with dying, there will be no rotting corpses in the streets, there will be no grief from the untimely death of loved ones. No, a lot less children will just be born.
Siena was afraid that people would understand the principle by which the virus was created and begin to produce bacteriological weapons. She decided to destroy the virus, but was late. The day marked by Zobrist was not the time when the virus will be released, but the date by which all of humanity will be infected.
The boss understands that Sinsky will not let him go with impunity. He organizes another hoax and tries to escape, but he does not succeed - the boss is arrested.
Sinski is trying to prevent panic.
Faster than the virus, only fear spreads.
Langdon leads Siena to Dr. Sinsky. The girl tells the head of the WHO about the virus, which made a third of the world's population barren. Zobrist's letter is destroyed, but Siena has an absolute memory, and Langdon convinces Sinsky to talk to the girl. She acknowledges the correctness of the Zobrist and agrees to cooperate with Siena.
If we neutralize the virus ... without having a feasible alternative plan, we just get everything back to square one.
Sinski takes Sienna to a medical forum in Geneva. Langdon escorts them. After kissing Siena, the professor hopes that everything is ahead of them.