Inferno by Dan Brown is the fourth installment in Brown’s Robert Langdon series of mystery/thriller novels, following (in order) Angels & Demons, The Da Vinci Code, and The Lost Symbol, and preceding Origin. Each edition covers a self-contained story, so readers need not follow the series in order, and often includes themes centered on European and Christian history and cultural traditions. The title character, Robert Langdon, is the only recurring character. Inferno won the Goodreads Choice Awards Best Mystery & Thriller in 2013 and was adapted into a feature film in 2016, directed by Ron Howard and starring Tom Hanks as Robert Langdon.

The book’s title is a reference to Inferno, the first part of Dante Alighieri’s three-part epic poem Divina Commedia, or Divine Comedy in English, which was completed in the year 1320 and traced Dante’s fictional pilgrimage through the three realms of the afterlife: Inferno (Hell), Purgatorio (Purgatory), and Paradiso (Heaven). Written in the 14th-century Tuscan dialect, the Divine Comedy is credited with establishing the modern Italian language, and Dante Alighieri remains one of the most important writers in the history of Italian literature. Textual and thematic references to Inferno abound in Brown’s novel.

This study guide refers to the 2013 Doubleday hardcover edition.

Content Warning: Inferno depicts violence throughout and includes a scene of sexual assault. This study guide quotes and obscures the author’s use of a derogatory reference to a Romani person.

Plot Summary

The majority of Dan Brown’s Inferno is told in the past tense third person from the many points of view of an ensemble cast of characters but mostly from that of Professor Robert Langdon. At the beginning of the novel, Langdon awakens in a hospital in Florence, Italy with no recollection of how he got there or the last few days. As Langdon attempts to get his bearings, an assassin named Vayentha arrives at the hospital and shoots his attending doctor in the chest in an attempt to break into Langdon’s room, but Langdon escapes with the help of a young British doctor named Sienna Brooks. Vayentha is revealed to be an agent of The Consortium, an independent, international organization focused on providing special ops to the highest bidder regardless of that bidder’s intentions. The Consortium is led by “the provost,” an unnamed character who leads the organization from a yacht-turned-mobile command center, The Mendacium.

Following his escape from the hospital, Langdon is taken to Sienna’s apartment, where he discovers her history as an ostracized genius child, and he attempts to piece together what has happened to him. He discovers a Faraday pointer in his coat pocket, which reveals a projection of Botticelli’s Map of Hell, based on Dante’s rendition in Inferno. From clues placed on the Map, Langdon eventually deciphers a message: “cerca trova,” Italian for “seek and ye shall find.” The phrase is famously painted in the background of The Battle of Marciano by Giorgio Vasari, which hangs in the nearby Palazzo Vecchio. As Langdon and Sienna make their way across Florence to the Palazzo, they are pursued by soldiers led by a man named Brüder, who Langdon also assumes is trying to kill him.

Once at the Palazzo, Langdon deciphers the clue in Vasari’s painting as pointing him to Dante Alighieri’s death mask, also typically on display at the Palazzo, but the mask is missing. Langdon discovers that he was at the Palazzo the night before with a colleague, Ignazio Busoni, and the two were captured on camera stealing the death mask after apparently locating another clue. Langdon and Sienna also learn that the death mask has been under the private ownership of an infamous biochemist named Bertrand Zobrist, who Sienna explains once proposed radical, violent methods for solving a perceived global overpopulation problem. From a message left by Busoni, who died the same night, Langdon concludes that the mask has been moved to the Baptistry of San Giovanni across the city. He and Sienna encounter Vayentha as they leave the Palazzo, and Sienna kills Vayentha.

At the Baptistry, Langdon and Sienna locate Dante’s death mask and discover a riddle poem written on the inside by Zobrist. The poem implies Zobrist has planted a biological weapon in a secret location with the intention of releasing a plague of his own design, meant to kill billions of people. Langdon and Sienna are then met by an ill man named Dr. Ferris, who claims to have originally brought Langdon to Florence, and the trio decipher from the riddle that they must go to Venice. On the way, Dr. Ferris is shown contacting the provost, and the story heavily implies that Ferris is complicit in Zobrist’s plot, having once been lovers with him. In Venice, Sienna reveals Ferris’s treachery just before Langdon discovers that Zobrist’s plague is in Istanbul. After making this discovery, however, Langdon is captured by Brüder and his soldiers, though Sienna escapes.

Langdon is brought aboard The Mendacium, where the true plot is revealed: Langdon had been brought to Florence by Dr. Elizabeth Sinskey, the head of the World Health Organization and an adversary of Zobrist, to decipher Zobrist’s Dante-related clues so Sinskey and Brüder could contain his plague. Instead, Langdon was intercepted by the provost and The Consortium, who had been hired by Zobrist to hide his work from Sinskey. The provost, ignorant of Zobrist’s plan, attempted to locate Zobrist’s work themselves by drugging Langdon and convincing him that Brüder was trying to kill him, thus motivating him to find Zobrist’s virus—a plot that, to Langdon’s horror, Sienna helped execute. It is revealed that Sienna, not Dr. Ferris, was Zobrist’s lover and the inspiration for his plague, which he named Inferno.

Fearful that Sienna intends to release the plague on her own, Langdon joins Sinskey, Brüder, and the provost (who allies with the others following the discovery of Zobrist’s plot) in traveling to Istanbul, hoping to find Inferno before Sienna. They track Inferno to Istanbul’s ancient cistern, but they are too late, and the virus is released. When Langdon discovers that Sienna is also present in the cistern, he chases her across the city. She almost escapes but turns back when she realizes she has nowhere else to go. Remorseful, Sienna confesses that the Inferno virus will not kill billions but instead will randomly render one-third of the world’s population infertile. And since the virus embeds in the germline, it will also render one-third of unborn humans infertile as well. As a result, the human population will decrease over time, thus avoiding what Zobrist saw as an inevitable environmental collapse. Sienna, fearful of what the governments of the world might do with Zobrist’s technology, had not intended to release Inferno but to hide it.

After the crisis abates and it becomes clear that Zobrist’s weapon was not a world-killing plague, Dr. Sinskey announces there will be a summit of global health leaders in Geneva to address how and if the world should reverse the effects of Inferno and invites Sienna to join her. After Sienna and Langdon part ways, Langdon returns to Florence to attend Ignazio Busoni’s funeral and returns Dante Alighieri’s death mask to the Palazzo Vecchio.