The Quest for the Sangraal was a search for the mythical "Sangraal" believed to actually be an Ancient device invented by Merlin, which can kill the ascended Ori. Meanwhile, the Ori have launched a bloody crusade to convert the galaxy to forcible worship, and SG-1 hopes that if their "gods" are destroyed their followers will cease their campaign.
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The Tau'ri finally has a solid lead on where the Merlin's anti-Ori weapon is, but Osric refuses to show them the map that Morgan left behind, as the last group of travelers who was the last System Lord Ba'al and his Jaffa loyalists which tried to steal it. (SG1: "The Quest, Part 1", "The Quest, Part 2")
The team visits a medieval like village near that world's Stargate, where they meet Osric, a frail librarian who keeps watch over the entire village's material related to the Sangraal. But they aren't the only ones looking for it. Lord Ba'al is also searching for the device, having passed through three days before. Osric warns them that many have come to him looking for the Sangraal, and have never returned from their quest. The way is perilous (the woods in which it is said to be located was cursed by Morgan Le Fay), and the legendary prize is guarded by a great dragon. Lt. Colonel Samantha Carter doubts that it's an actual dragon, believing it to be some form of advanced security system. Furthermore, an ancient scroll known as the Parchment of Virtues advises that seekers of the Sangraal must possess five virtues: prudence, charity, kindness, wisdom, and faith.
At that moment Ori soldiers storm the city and declare the planet under Ori rule. With the help of a local Barkeep, the team manages to escape the Ori troops, and convince Osric to lead them to the Sangraal. While moving closer to the forest, the team is surprised to find dozens of Jaffa soldiers frozen in time. Carter explains that the people are trapped in a time dilation field and a small corridor of real time leads further into the bubble. Using a special meter and by throwing rocks, the team manages to successfully navigate the maze. As they continue forward, they are greeted with a surprising sight. Ba'al, who was the ruler and last remaining high racking member of the Goa'uld Empire; abandoned by his own Jaffa loyalist force and looking very put-out. The team confronts Ba'al, but fall into a trap. Ba'al reveals that he was lured here by a chest lying on the ground and was trapped for three days inside a powerful shield, and now the team is trapped inside as well. Daniel then realizes that they must follow the five virtues literally. The team used prudence to navigate the time dilation maze, so the obvious answer is to use charity to escape. Each person places an item of value inside the chest and the shield deactivates. The team is about to kill Ba'al, but he informs them that he knows the dragon's true name, which may be an important password or access code, convincing the team to bring him along.
However, as they continue on their journey, Daniel suddenly confronts Osric. After observing him for some time, Daniel suspects Osric to be a spy for the Ori. Osric smiles and reveals himself to be Adria in disguise. She tells the team that all of the events leading up until now were orchestrated by her to make the team lead her straight to the Sangraal, including Vala's dream at the beginning of the episode. She then forces Daniel to help her find the weapon or she will kill the rest of SG-1. Daniel reluctantly agrees. They then enter a cave and find a small boy trapped in a cage. The team uses the virtue of kindness to open the cage, and a secret passage is revealed. They then use the virtue of wisdom to solve a series of riddles as the cave begins to collapse. Finally, the team arrives at a huge wall of fire, and are seemingly stumped on how to continue.
Daniel, however, is convinced that he knows the way through. He uses the final virtue, faith, and walks through the wall of the flames. The flames disappear to reveal the Sangraal. Adria orders Daniel to take it and give it to her, but Daniel realizes that while inside the cavern, Adria cannot use her Ori abilities. He challenges her to take the Sangraal herself, but she refuses. He then attempts to pick it up himself, but it is just a hologram. Suddenly, the door behind the team closes shut and a massive dragon appears, breathing fire and poised to attack the team.
The dragon attacks by breathing fire but Adria extends her personal shield to protect the team. SG-1 attempts to engage the dragon, but their firearms have no effect. The dragon swings its tail and knocks open an opening in the wall, through which the team escapes. Thinking they are momentarily safe, Lt. Colonel Cameron Mitchell soon sees a fireball expanding into the tunnel, and commands the team to run. They are able to find a way outside, but the dragon bursts out of the top of the mountain in pursuit.
Mitchell decides that since the prior attempt to fire on the dragon failed, that perhaps a different method of attack would be more successful. He reasons that "bullets don't bounce off Holograms" and decides to use C-4, believing the dragon to be solid matter. They take cover in the tree line while preparing the attack, but Dr. Daniel Jackson states that they have to defeat the Dragon as it is the final task, and that speaking the Dragon's true name will destroy it. Vala Mal Doran suggests it might be Darrell the Dragon, while Teal'c suggests Puff. Ba'al had previously stated that he knew the name of the guardian, but admits that this was a lie. Mitchell, having prepared the C-4, plans to run into the clearing and lure the dragon to the ground, giving him the opportunity to use the C-4 against the dragon's vulnerable underbelly. He prepares to run into the clearing, but is restrained by Teal'c, who silently convinces Mitchell that he should be the one to act as the bait. The plan is initially a success; the Dragon lands and Teal'c throws the C-4 into the dragon's mouth. Lt. Colonel Samantha Carter hits the detonator and a faint light is seen in and around the dragon's mouth but to the dismay of the team the dragon is unaffected, and proceeds to chase Teal'c.
As Teal'c begins to run back, Daniel reasons that the guardian referenced in the scroll is not the dragon, but the individual who created the dragon: Morgan Le Fay. Vala runs out, with Daniel in pursuit, telling her to wait. Vala stops in front of the dragon and says "Morgan Le Fay" but the Dragon remains. In desperation, she questioningly states "Darrell?" which predictably has no effect. Daniel catches up and quickly says "Ganos Lal" (the Ancient name of Morgan Le Fay) and the Dragon disappears.
The group returns to the mountain and surround the Sangraal. Daniel reaches for it, and they are transported to another chamber. However, they discover that Adria was not transported with them. Daniel and Carter assume it was a failsafe to stop the wrong people coming, to which Mitchell complains that Ba'al remains with them. Upon inspection of the cave they find a frozen body with an inscription: "Here lies Myrddin, archmage of the round". Daniel announces that the tests weren't designed to protect the Sangraal, they were designed to protect Merlin, who is in a stasis pod similar to the device in which Colonel Jack O'Neill was frozen in Antarctica. Morgan would have had to destroy the Sangraal that Merlin had created, or risk the wrath of the Others, so she did, but preserved Merlin in the hope that he would be able to reconstruct it. Vala looking around the cave a bit more, comments to the team about a fixture on the wall, Daniel quickly tells Vala to watch out as the Ancient Repository of knowledge tries to grab Vala, she successfully evades.
Merlin is released from stasis, and mistakes the party for some of the Knights of the Round Table. Ba'al begins to complain and Merlin literally silences him with a wave of his hand. Daniel explains that they are not the Knights and also the current situation with them and the Ori. Vala and Daniel remain with Merlin while the rest scout the area. They discover that they have changed locales and now find themselves in a desert environment not the verdant environment they were in prior. Teal'c remains outside while the others head back in to tell Vala and Daniel the news.
Back in the village, Adria is angry that SG-1 and Ba'al has evaded her, and that they may be en route to finding the Sangraal. The Prior tells her that when travelers beamed away, the Stargate opened for a split second. Adria orders the burning of the town, and attempts to discover where group has gone by examining the Dial Home Device.
Merlin agrees to help build a new Sangraal, but asks one thing in return: that they follow him, and whatever happens, they must allow it to happen. Merlin stares into the Repository of the Ancients, which causes a 3 dimensional hologram to appear. Within the virtual space, Merlin begins to assemble the Sangraal. The team watching Merlin observes a strange shift, and Teal'c advises that the team should come outside. Mitchell with Ba'al and Carter arrive outside and discover that they are now on a Snow Planet. Carter reasons that to keep one step ahead of any pursuer, Morgan has programmed the gate to dial out every few hours and move the team from planet to planet on a network outside the standard gate network. Carter and Ba'al are told to work on the device so that they can figure a way to dial out from the gate. Merlin constructing the Sangraal. Hours later, Merlin is weakening with the stress of building the device, and insists he rest. Daniel tells him to take all the time he needs, but reminds him of what is at stake. Merlin muses to himself that he is too old and that there is not enough time and faces the Repository of the Ancients once more. A blinding white light comes from the device, and Merlin is thrown back to the ground dead.
Shocked at what has just happened, Daniel wonders about Merlin's final words, but realizes that Merlin must have uploaded his knowledge into the Repository of knowledge. Although O'Neil's previous encounters with the device had proved almost fatal and required intervention by the Asgard to save his life, Daniel speculates that Merlin had used the Repository to store only a limited amount of information, so as to not overwhelm the human brain. He faces the Repository of the Ancients, which downloads Merlin's knowledge into Daniel. Vala contacts Mitchell and tells him to come back quickly; he tells the others to remain outside working. Mitchell, upon returning sees Daniel lying unconscious with Vala holding him. After a while Daniel regains consciousness, holding his head in his hands. Mitchell asks if he is alright and Daniel replies as if he is Merlin, stating that Mitchell really is similar to Perceval. Mitchell and Vala realize that the Ancient knowledge is overwhelming Daniel. sees Daniel holding his head in his hands and saying that he will continue to build the device. Another shift occurs, leaving Merlin's body behind. The team outside confirms that they are now on a jungle planet, pleasing Ba'al who did not enjoy working in the cold. However Adria is not far behind. She is able to deduce the gate address from the DHD after some study, and travels from the desert planet to the snow planet. Her guards also find Merlin's body, and Adria begins work on deciphering the next address, stating that each time it is taking her a shorter period to find the address.
Daniel, moving at a much greater speed that Merlin was able to, completes the first stage of the Sangraal device in the holographic space, which then beams into existence on the pedestal below the hologram. He staggers from the repository weakened and states he must rest. He returns to the repository and continues with the Sangraal. Carter and Ba'al disagree about how to use the DHD to leave the planet. Carter reasons that, since they can't find a dialing program in the DHD, it must be stored in the obelisk that is next to the gate. Ba'al dismisses the idea as ridiculous because Carter is a human and, worse still, a woman.
Mitchell and Vala realize that the Ancient knowledge is overwhelming Daniel. Vala begins to worry about Daniel's safety, and challenges Mitchell to tell Daniel not to continue. Mitchell reminds her about the time she flew into the Supergate and tells her that, "Now you know the hard part about being part of this team is not risking your own life, it's watching your friends take chances with theirs'. Congratulations. Now you really are one of us.". Ba'al once again mentions that since Carter is a woman, she can't do much when she has trouble locating the automatic dialing device in the obelisk. Carter punches Ba'al, knocking him to the ground, and advises him that if he refuses to help, then he's no longer worth keeping around. His life now in the balance, Ba'al becomes cooperative.
Daniel completes the second stage of the Sangraal and again steps away from the repository exhausted. Mitchell asks how many more stages there are and Vala says that she thought the red crystal was the Sangraal. But it is actually the final stage of it, the thing that makes the whole weapon work. Carter, struggling with the piece she believes is a way to activate the gate and leave the planet, reluctantly asks Ba'al for help with it. With a smiling look, Ba'al asks why he should help her; Teal'c reminds the System Lord of his current situation and he agrees. They are able to disable the safeguard preventing them from dialing out, but before they can act, an incoming wormhole registers. Carter informs Mitchell, and he and Vala head outside, while Daniel continues to rest. Adria's guards come through the gate and the team open fire. Mitchell and Vala arrive for support; Ba'al is shot.
Adria arrives in the cave, finding the incomplete Sangraal and proclaiming her victory to Daniel. Daniel uses his new powers to create a lightning storm killing the Ori guards. The team turns to see Daniel flung from the mouth of the cave, with Adria standing triumphantly above. Carter dials out and the team are ready to leave, but Adria uses her power to fire a stream of energy at the team. Daniel uses his powers and creates a force field to protect his friends who head to the gate. Mitchell walks through, and Adria overwhelms Daniel, who collapses. (SG1: "The Quest, Part 1", "The Quest, Part 2")
Back at Stargate Command, Vala is looking for a way to go back and rescue Daniel, but the team is unable to determine the address from which they dialed in. Vala, frustrated, comments that Adria didn't have any trouble.
Aboard an Ori warship flying through hyperspace, Daniel sits on the floor of a dark room. Adria enters, and he claims that whatever he had is gone, but Adria doesn't believe him. She advises Daniel to rest, because there is much to be done.(SG1: "The Quest, Part 1", "The Quest, Part 2")
With the help of Merlin's consciousness, Daniel is eventually able to trick Adria into believing he is on her side and she converts him into a Prior to convert Earth and finish the weapon so the Ori can use it to destroy the Ancients. Using a complex plan and with the help of the rest of SG-1 and General Jack O'Neill, Daniel finishes the weapon and deploys it to the Ori galaxy, killing the Ori though that is unknown for sure for some time. (SG1: "The Shroud", "The Ark of Truth")