Caligula [Malcolm McDowell] is the young heir to the throne of his great-uncle, Emperor Tiberius [Peter O'Toole]. One morning, a blackbird omen appears in his room, setting an uneasy mood that mirrors the looming shadow of power. Soon after, Naevius Sutorius Macro [Guido Mannari], one of the Praetorian Guard chiefs, informs Caligula that Tiberius demands his immediate presence at Capri, where the Emperor lingers with his close friend Nerva [John Gielgud], Caligula's dim-witted uncle Claudius [Giancarlo Badessi], and Caligula's cousin Gemellus [Bruno Brive]. Fearing assassination, Caligula hesitates, but his sister and lover Drusilla [Teresa Ann Savoy] urges him to travel.
On Capri, Caligula witnesses a Rome in decline through Tiberius’s debauched pleasures and embittered view of politics. He watches as the Emperor swims naked with youths and endures humiliating sex shows, a tableau that fascinates and horrifies him at the same time. Tension heightens when Tiberius attempts to poison Caligula in front of Gemellus; Nerva meets a tragic end when he takes his own life, and Caligula’s first attempt to strike back fails. Macro proves his loyalty by killing Tiberius, with Gemellus bearing witness to the brutal act.
Following the death and burial of Tiberius, Caligula is proclaimed the new Emperor and immediately elevates Drusilla to a position of equality, a move that unsettles the Senate. Drusilla, wary of Macro’s influence, pressures Caligula to remove him from power. Caligula stages a sham trial in which Gemellus testifies that Macro murdered Tiberius, and he bans Macro’s wife Ennia [Adriana Asti] from Rome. Macro is publicly executed in a gruesome game, while Caligula appoints Longinus [John Steiner] as his personal assistant and elevates the previously compliant Chaerea [Paolo Bonacelli] to lead the Praetorian Guard.
Drusilla seeks a marital match for Caligula with Isis priestesses, but Caligula’s desire to wed her is blocked by the fact that she is his sister. Instead, he marries Caesonia [Helen Mirren], a priestess and noted courtesan, who bears him an heir, and Drusilla reluctantly supports the arrangement. While the people momentarily applaud Caligula’s charisma, the Senate remains wary of his eccentricities. Darker impulses surface when Caligula brutishly violates a bride on her wedding night and orders Gemellus’s execution to provoke a reaction from Drusilla.
When Caesonia becomes pregnant, Caligula falls seriously ill. Drusilla nurses him back to health, and Caesonia soon bears a daughter, Julia Drusilla. As Caligula recovers, Drusilla dies from a fever, plunging him into grief. He roams the streets in disguise, disturbed by a street performance that mocks his relationship with Drusilla, and ends up briefly jailed before proclaiming himself a god and targeting Rome’s senatorial class. He desecrates old religions, confiscates estates, and orders the army to stage a mock invasion of Britain, bringing the empire to a breaking point. Longinus and Chaerea plot to end his tyranny, driving a coup that will reshape the Roman world.
The coup culminates in Caligula’s bedroom, where Caesonia awaits and a second blackbird omen appears. They rehearse a simple Egyptian play, but the palace erupts as Claudius [Giancarlo Badessi] suspects Chaerea and follows him to the confrontation. In the ensuing chaos, Caesonia and Julia are murdered, and Chaerea fatally stabs Caligula. With his last breath, the Emperor defiantly whispers I live! as his family’s bodies are cast down the stadium stairs. Claudius, shaken but resolute, is proclaimed Emperor by the Praetorian Guard, and the Roman people, now numb to the spectacle of power, begin to clear the stains from the marble floors. The film closes on Incitatus, Caligula’s horse, calmly rinsing the blood from the sites where the tragedy unfolded.
