"The Fall of Centauri Prime" is an episode from the fifth season of the science-fiction television series Babylon 5. This is a key episode in the series, as it marks the final downfall and story completion of Londo Mollari, one of the major characters on the series.
As the episode begins the combined Narn and Drazi fleets are bombarding Centauri Prime from space. On the surface explosions and fires rage across the planet's capital city. In the Royal Palace, Prime Minister Londo manages to get G'Kar out of his prison cell just before the ceiling collapses; G'Kar is slightly injured but manages to walk with Londo back to a room in the palace itself.
Desperate to stop the attack on his homeworld, Londo searches for and finds the Regent. He discovers that the Regent has been under the secret control of a sinister alien race. The alien race are called the Drakh. The Drakh were "dark servants" of the ancient Shadows, and lived with the Shadows on their homeworld of Z'ha'dum. When that world was destroyed, the Drakh needed to find a new homeworld, and they decided to settle on Centauri Prime. They remembered the Centauri homeworld from the time they spent there under the protection of the psychotic Emperor Cartagia. However, the Drakh did not want their presence on Centauri Prime to be discovered, and so they live underground, beneath the Royal Palace and the capital city. Shortly after arriving they took control of the Regent by placing a creature called a "keeper" on his shoulder; the keeper is telepathically linked to the Drakh and can control the Regent's mind when it wishes. It also has the ability to stay invisible; thus no one knows that the Regent is under their influence.
Having explained themselves to Londo, the Drakh then make their demands: they will be allowed to remain on Centauri Prime, they will remain in covert control of the Centauri government, and they will take the Centauri Republic out of the Interstellar Alliance. By doing this the Centauri will be left alone in the galaxy, with no friends or allies, and thus the Drakh will have no one to interfere with them. When Londo refuses their demands, they tell him that they have planted nuclear fusion bombs underneath the planet's major cities, and that unless Londo agrees to their terms they will detonate the bombs, killing billions of people and completely destroying what is left of Centauri civilization. Realizing that he has no choice, Londo agrees. The Regent's keeper then detaches itself and the Regent dies, thus placing Londo in line to become the Centauri Emperor the next morning. However, the Drakh insist that Londo accept a "keeper", so they can control him as they did the Regent. Again having no choice, Londo agrees.
Meanwhile, President Sheridan arrives at Centauri Prime with a small fleet of White Stars and orders a ceasefire. The Narn and Drazi reluctantly agree to halt the attack, but ask Sheridan to aid them when the Centauri fleet returns and attacks them for what they have done. Sheridan refuses, but knows that he may have no choice but to fight. In another region of the galaxy, Sheridan's wife Delenn and her aide Lennier are trapped in their heavily damaged White Star after a Centauri attack. The White Star is still in hyperspace and gradually drifting away from the main beacon; if it drifts too far off the beacon it will be permanently lost.
Londo goes to G'Kar to ensure that he is OK and to say goodbye. Londo tells G'Kar that he is about to become the emperor and that G'Kar can no longer serve as his bodyguard. He does not tell G'Kar about the Drakh or that they secretly caused the war between the Interstellar Alliance and the Centauri. Londo then accepts the keeper, which uses its tentacles to attach itself to his shoulder and becomes invisible. Londo then issues an order to the returning Centauri fleet to stand down and not attack the Narn/Drazi fleet. Sheridan contacts Londo and asks to come down to the planet and speak to him. Londo at first refuses, but finally agrees when Sheridan informs him that Delenn is missing. In their meeting, Londo is surprisingly rude and arrogant towards Sheridan, informing him that he will help to find Delenn only out of charity, not because of their friendship. Sheridan angrily responds that since the Centauri lost the war, they will be expected to pay heavy reparations to the Interstellar Alliance. Back in the privacy of his quarters, Londo begs the Drakh leader to save Delenn; it is obvious that he still cares for his friends but can no longer show it due to the keeper's influence over him.
Delenn's White Star has run out of fuel, and as a last desperate act she fires the ship's weapons to attract the attention of anyone nearby. A group of Centauri warships converge on her position. At this point Lennier, believing that they are about to die, admits his love for her. Instead, the Centauri vessels take their ship in tow and they are saved. To spare Lennier from humiliation, Delenn pretends that she didn't hear him earlier when he confessed his love. Delenn and Lennier are taken to Centauri Prime, where they meet Sheridan and G'Kar. Vir Cotto, Londo's longtime aide on Babylon 5, also arrives; he bursts into Londo's palace room and is angrily told by Londo to never surprise him like that again. Londo is worried that Vir will see him with his keeper, and that the keeper will force him to kill Vir.
Sheridan, Delenn, and G'Kar plan to attend Londo's inauguration as Emperor, but Londo gives an angry speech to his people in which he attacks Sheridan and the Interstellar Alliance and tells them that the Centauri are now "alone in the universe." In the background, out of sight, the Drakh leader smiles as he listens to the speech; Londo is saying exactly what he wanted. Londo announces to his former friends that he will go to his installation as emperor alone, and that they are not welcome. Although puzzled by Londo's behavior, they reluctantly agree and return to Babylon 5. In his first official act as emperor, Londo names Vir as the new Centauri Ambassador to Babylon 5.
On Babylon 5, the command staff and leadership of the Interstellar Alliance examines a piece of Shadow technology and wonders how many other ancient weapons and artifacts the Shadows and Vorlons left behind. Garibaldi suggests going to the Vorlon homeworld to recover useful items, but automatic defenses have apparently destroyed all ships that attempted to land on the planet, and telepath Lyta Alexander tells the group that no one will be allowed on the Vorlon homeworld for a million years, until humanity is ready to use such advanced technology.
In the Centauri Royal Palace, Londo sits alone and silent on his throne. Behind him the capital city continues to burn from the Narn/Drazi attack. It is the ultimate irony when Londo states that once, I had all the choices in the world, but no power at all, but now, I have all the power in the world, but no choices at all.