Teaser : The Jumpgate opens and an Earth passenger ship, the Asimov, appears flying towards Babylon 5. In C&C, Sheridan and Ivanova are discussing how they are going to finance the station's operation now that they are independent. Docking credits are the largest part of their income and they cannot rely on the Minbari for ever for their defence. Some others have found solutions to the financial problem already: At the Post Office, Garibaldi is asked to pay 100 credits to retrieve his last food parcel from Earth. Costs have increased, or so the Postmaster claims. Inside the Asimov one of the passengers sleeps fretfully, plagued by nightmares. In his dreams, he is running in a corridor opening to many doors. One of the doors opens to a place where wind blows like a terrible storm. Another door opens to what seems like a battle, with blinding explosions. The man flees to the end of the corridor where a shinning sword hangs in the air and the man takes it, relieved.
In Downbelow, Dr. Franklin is examining some Banta flu patients that Marcus was able to identify early by noticing that they were eating a contaminated food, thus preventing a possible outbreak. As Dr. Franklin and Marcus discuss about the unfairness of many of the Lurkers' situation Marcus says:
Marcus : You know, I used to think it was awful that life was so unfair. Then I thought, "Wouldn't it be much worse if life were fair? And all the terrible things that happen to us come because we actually deserve them?" So now I take great comfort in the general hostility and unfairness of the universe.
As they reach Medlab with the two worse off patients, Dr. Franklin asks Marcus about the Ranger pin that Marcus is wearing. Marcus explains that the two sitting figures embracing the jewel in the centre are one Human and one Minbari, blending together in the middle to signify the two halves of their souls uniting against the common enemy. The jewel is the Isil'zha, meaning "the future" and also "the beginning", among other things. Marcus also explains some of what he learned from the Minbari: the importance of knowing the other's language in order to understand how to win a battle, as well as delight, respect, compassion, how to make one's action pure from direction, determination, patience and strength. They taught Marcus how to live, breathe, fight and die, and also how to use and face terror.
Walking back together, Dr. Franklin and Marcus pass by customs where an incident is taking place: A passenger from the Asimov has triggered the scanners and the security guards are asking him to hand over the sword that he is carrying. The man refuses, identifying himself as King Arthur, returning from Avalon with Excalibur. To avoid the escalation of violence, Marcus kneels in front of Arthur and in his best British accent tries to convince him to lower the sword and follow him and Dr. Franklin to Medlab for an examination. Playing to his delusion, Marcus pacifies Arthur and he obliges. In Medlab, they go over his belongings and discover that he has no identification, probably because he threw it away while on board of the Asimov. DNA and prints will have to be used. Dr. Franklin interrogates him but he claims that his last memory was that of the battle of Camlan and the death of all his knights except Sir Bedivere, who was supposed to return Excalibur to the Lady of the Lake, so that Arthur himself could be taken away to be healed at Avalon, from where he would return when he was most needed.
Dr. Franklin and Marcus are discussing the new arrival with Sheridan and Garibaldi. Sheridan tries to dismiss the possibility of the man really being Arthur, but Marcus insists that it is possible. The Vorlons could have taken an ancient king and returned him now, as they have done with other humans in the past, perhaps to use him as an inspiration. Dr. Franklin points out that the man's speech is too contemporary, so he is probably just deluded. The question is why this particular delusion. As they are talking, a message comes for Dr. Franklin on the link to inform him that Arthur has escaped. He is now walking in a marketplace in Downbelow, where he approaches an elderly woman who is crying. He kindly asks her what is the matter and she explains that some thugs have stolen her late husband's portrait, her last precious possession, probably to sell the frame. With gentle words he consoles her and asks her for the whereabouts of the thieves. Nearby, G'Kar is dealing with a smuggler that passes on messages between the Narns in the station and their families back in their homeworld. They hear a scuffle and from a balcony they see four thugs assaulting a man. Neither of them intervenes until Arthur appears, sword in hand, and demands the return of the portrait. He beats them up, with an admiring G'Kar as an audience, but more thugs appear from behind. That prompts G'Kar to intervene in favour of Arthur and they face their enemies, sword and claws together.
Later on, Arthur and G'Kar return the portrait to the old lady and adjourn together to a pub for some celebratory drinking while Arthur explains to G'Kar the principles of Chivalry and of the Round Table, ending up knighting G'Kar as the Red Knight. Meanwhile, Garibaldi sets up a search team for Arthur, considering him armed and dangerous, something that Marcus overhears. Garibaldi himself goes with one of the guards to break into the Post Office and retrieve his package, only to be stopped by the Postmaster who seems to sleep on the premises. They have battled Earth Marines hand-to-hand, but they would not lay a finger on Post Office employees. There are lines that are too dangerous to cross. Back in the pub, G'Kar is getting thoroughly smashed while Arthur explains what happened after the battle of Camlan, when he lied injured and witnessed his fallen comrades being robbed by scavengers. He felt that he was responsible for their deaths. As he says this, the same images from the nightmare, the door opening to a battlefield, reappear, but this time it is possible to identify a Minbari cruiser shooting down a Starfury. Prompted by G'Kar, he then explains that the battle of Camlan was a mistake, a meeting to arrange a truce gone wrong when one of the knights unsheathed his sword to kill an adder. Arthur is clearly upset by this remembrance. Marcus joins them and convinces Arthur to return with him to Medlab to avoid further trouble.
Sheridan has called a meeting of the Babylon 5 Council to explain to the representatives of the League of Non-Aligned worlds that they are going to need their help to keep Babylon 5 open as neutral territory for commerce, travel and eventually negotiation among the warring factions. They ask the representatives to provide ships for the defence of the station and propose that they sign what they call the Babylon Treaty, which would replace any former treaty signed with Earth regarding the station. They adjourn to think it over. Back in Medlab, Dr. Franklin has managed to track down Arthur's real identity from his DNA samples and, despite Marcus' strong objections, decides to confront Arthur with them. He shows Arthur his file but Arthur does not even recognise his own picture. His real name is David McIntyre, 52, a decorated veteran of the Battle of the Line where only one out of 2.000 soldiers survived. But before that, he was gunnery sergeant on the Prometheus, the first ship that encountered the Minbari exactly fifteen years earlier. Misinterpreting their intentions, the Prometheus opened fire against the Minbari destroying two of their ships and killing the Minbari leader Dukhat. He was the soldier who, following orders from the captain, pulled the trigger and started the Earth-Minbari war. Arthur/David cries out that it was an adder at Camlan but when Dr. Franklin insists that he was exonerated of any wrongdoing to try to break through the delusion, Arthur/David mixes the old battle with the new and finally blames himself for causing both and for surviving. In his dream, he reaches for the sword, but a black night strikes him from behind, leaving him in a catatonic state both in his dream and in reality.
In C&C Ivanova informs Sheridan that although not all of the League members have signed the Treaty, enough of them to ensure Babylon 5's defence have. In Medlab, Dr. Franklin blames himself in front of Marcus for trying to fix everything just to make things worse. Arthur/David is lying in a bed with the sword clasped in his hands, but does not look like he is ready to come out of his catatonia. Marcus is more concerned with solving the puzzle of Arthur/David's presence on the station. Even in his delusion, there must be a reason for his coming here. They analyse the Arthurian legend, looking for clues, and discuss again the end of the battle of Camlan, when Arthur asks for the sword to be returned to the Lady of the Lake so that he can be healed. If the sword, according to his previous ramblings, represents the weapon that caused the war, in this case the Prometheus, and also the king's pain and burden, the act of giving it to the Lady of the Lake means that he is forgiven and can begin to heal. But who is the Lady of the Lake?
In Arthur/David's room in Medlab, Delenn approaches the prostrated figure of the fallen warrior clutching the sword. As she touches his hand, between dream and reality Arthur/David gives Excalibur to Delenn and finds the forgiveness that he needed in her Minbari eyes.
At the Post Office, Garibaldi is paying the outrageous 100 credit fee demanded by the Postmaster and manages to get his hands on his package. But there is retribution: Earth is no longer paying rent for the space occupied by the Post Office in the station. Now, Garibaldi would overlook that because of the public service that the Post Office offers in exchange for, let's say, 101 credits? Back at customs, David is leaving to help the Narn Resistance organise help and support for those in need as per the old Chivalry codes, like a new Round Table. G'Kar and Dr. Franklin come to say their goodbyes. Marcus joins Dr. Franklin afterwards and they discuss the potential parallels between the Arthurian characters and the station personnel. Kosh is Merlin, Dr. Franklin is Percival, Marcus is Galahad, Sheridan is Arthur, Ivanova is Gawain, Mordred, well, no need to say who, but they are missing one: Who is Morgana le Fay?