In G.K. Chesterton’s otherworldly spy novel The Man Who Was Thursday, the poet, philosopher, and police detective Gabriel Syme infiltrates a vast anarchist conspiracy to save the world from its sinister plots. But when Syme learns that the other anarchist leaders are not who they seem to be, he starts questioning what his mission really meant in the first place—and who has been pulling the strings.
The novel begins in a garden in the quaint London suburb of Saffron Park, where the firebrand anarchist poet Lucian Gregory passionately lectures his friends about the evils of organized society and the beauty of destruction. When Gabriel Syme attends one of Gregory’s parties, they debate whether poetry is a form of order or chaos. Syme accuses Gregory of not being serious about anarchism, and in response, Gregory offers Syme “a very entertaining evening”—but only if he promises not to tell the police.
Gregory takes Syme to a seedy pub, where their table shoots down through a secret passageway into an underground anarchist bunker full of bombs and weapons. Gregory explains that his group wants to destroy all religion, government, and morality. He’s expecting the local branch to elect him to the Central Anarchist Council at its next meeting—which is in just a few minutes. Right before it starts, Syme tell Gregory that he works for the police. Gregory knows that, if he exposes Syme to the other anarchists, then Syme will expose him to the police. Instead, he lightens the tone of his election speech to try and convince Syme that his group is harmless. But this backfires: Syme challenges him in the election, gives a fiery speech promising murder and destruction, and wins easily. A tugboat carries him down the Thames to meet the rest of the Council.
A flashback explains how Syme became a detective. After growing up in a family of unstable nonconformists and witnessing a bloody anarchist attack, Syme decided to launch a “rebellion against rebellion.” When a police officer approached him and asked him to join a special new anti-anarchist unit, he signed up. Notably, the unit chief insisted on meeting him in a pitch-black room—and told him that he would die a martyr.
Syme gets off the tugboat at daybreak and meets the Secretary, a menacing man who can only smile with one side of his face. The Secretary takes Syme to meet the rest of the Council in central London’s Leicester Square. Since people assume that serious anarchists would never talk about anarchism publicly, the Council President has decided the group should plan their attacks in full public view, over breakfast on the balcony of a popular restaurant. Even though they know each other’s real names, the Council’s members use days of the week as pseudonyms. The imposing President is called Sunday, the Secretary is Monday, and Syme is now Thursday. Tuesday is an unkempt Polish malcontent named Gogol. Friday is an elderly nihilist philosopher named the Professor de Worms. Saturday is a lively young doctor named Bull, whose opaque black glasses make him seem like the wickedest of the bunch. And Wednesday, the French nobleman Marquis de St. Eustache, is planning to assassinate the Russian Czar and the French President when they meet in three days.
Syme notices Sunday staring at him throughout the breakfast. Then, Sunday calls the whole group into a private back room and announces that one of them is a traitor. Syme is certain that he’s done for—until Sunday identifies Gogol as the spy and kicks him off the Council. Relieved, Syme goes for a long walk and gets lunch. But he notices the decrepit Professor de Worms hobbling after him the whole way. Even when Syme sprints to catch a bus and intentionally gets lost in a maze of winding alleys, the Professor inexplicably catches up to him. When he finally confronts the Professor in a shady sailors’ bar, the Professor admits that he’s a police detective in disguise. Syme explains that he is, too. They start plotting together to stop the upcoming bombing. They develop a secret sign language and visit Dr. Bull, who’s planning the attack, at his garret. But when Syme asks Bull to take off his black glasses, he realizes that Dr. Bull’s shining eyes are far too innocent to be an anarchist’s. Surely enough, Bull works for the police, too. The three detectives head to France to stop the bombing.
Syme hatches a plan: he challenges the Marquis to a fencing duel, then makes sure to plan it on the morning of the Marquis’s train to Paris. If he misses the train, the Marquis can’t carry out the assassination. The Marquis agrees to the duel, on the condition that they hold it in a field next to the train station. But he doesn’t bleed or scar when Syme stabs him. Syme realizes that the Marquis is wearing a disguise—he, too, is a police detective. When the train pulls into the station, a group of anarchists wearing black masks gets off it and starts pursuing the four detectives, who borrow a peasant’s cart, an elderly innkeeper’s horses, and a local doctor’s motorcar to escape. But somehow, the anarchists win these three men and most of the local townspeople to their side. Led by the Secretary, the anarchists corner Syme and his companions on the beach. The detectives feel like the whole universe is united against them. But then, Syme gives an impassioned speech about the value of tradition and hits the Secretary with an antique Christian lantern. The Secretary reveals that he’s a detective, too—meaning that everybody on the Council worked for the police except the President, Sunday.
The detectives return to London, find Gogol, and confront Sunday over breakfast in Leicester Square. Sunday refuses to explain who he is or what he is doing—but he does tell them one secret: “I’m the man in the dark room, who made you all policemen.” He runs away, and a long chase scene ensues. At various points, Sunday escapes using a horse-drawn cab, a firetruck, an elephant, and a hot air balloon. The detectives chase Sunday to the outskirts of London, where his balloon has crashed in a field. On their way, they realize that Sunday looked different to each of them, but they all saw him as a reflection of “the universe itself.” Syme comments that, just like Sunday, reality is made of two opposite sides: “the horrible back” and “the noble face.”
Before the detectives can reach Sunday, an old man with a scepter approaches them and brings them to six carriages, which carry them up a magical hill to a grand celestial gateway. Beyond the gate, they put on new clothes that give new meaning to their pseudonyms: the days of the week now refer to the days of creation. For example, the Secretary (Monday) wears a black robe with a white stripe, which represents God creating light on the first day, while Syme (Thursday) wears a blue outfit with an image of the sun, which represents God creating the sun and moon on the fourth day. The six detectives meet at a carnival where figures dressed in animal costumes drink and dance around a bonfire. Sunday joins them, wearing pure white, and claims to be “the Sabbath”—or “the peace of God.” The detectives debate whether they can forgive Sunday for terrorizing them.
Suddenly, Lucian Gregory—the novel’s only “real anarchist”—arrives. He asks the detectives if law-abiding believers like them can truly suffer in the same way as anarchists who don’t believe in anything at all. But Sunday’s terror proves that Christians do suffer. Gregory asks Sunday the same question, and Sunday answers by quoting the Bible: “Can ye drink of the cup that I drink of?”
In the novel’s closing lines, Syme gradually becomes aware of his real-life surroundings again. Chesterton reveals that the detective drama has all been a fantasy—Syme has been taking a leisurely stroll through Saffron Park with Lucian Gregory the whole time.
