The Odyssey comes out of hyperspace in the Pegasus galaxy and arrives above Atlantis. Elizabeth Weir greats them as they arrive and tells them SGC wants them to start on their new mission right away.
SG-1 (minus Teal'c) meet with Weir's team and describe their plan to try to dial in with their Stargate and into the Ori supergate, but McKay is dubious. They plan to move a second Stargate near the Ori supergate and supply a huge burst of energy via nuclear warheads to force the gate to "jump" to the nearest portal – the supergate. Then they'll link it to a black hole to force the supergate to remain open, preventing the Ori from creating a new wormhole. Daniel and Vala will stay there at Atlantis to research their database for references to Merlin and the other planets while the others go on. Weir shows them the holographic interface
The Odyssey arrives at the black hole and drop off the stargate, while Daniel tries to track down the desired planet. Vala's suggestion to just simply ask straight out is successful, giving two sets of coordinates.
Sam establishes the wormhole to the black hole and they contact Teal'c at the Ori supergate. He's positioned the second stargate and they activate the nuclear warhead, but fail to make the connection.
Daniel is wondering why Vala's plan worked and how the database is translating a language 800 years after its original time. He checks the images of all the Atlanteans who fled to Earth.
McKay has concerns about the energy blowing out the stargate and Mitchell convinces him to try anyway. Daniel comes up with the picture of an Atlantean high councilor who matches the image of Merlin. The hologram system says the first human to enter the city was Weir, but he notices the discrepancy and asks who the first Ascended was. The "hologram" reveals she is actually an Ascended being, tells him he has his answer, and disappears.
McKay comes up with a plan to use a second bomb but they'll have to get closer, while Weir detects a Wraith ship approaching Odyssey. She contacts SGC who will get a ship near Teal'c's so he can relay it to Odyssey.
Daniel yells out to confront the Ascended, who he concludes was Morgan le Fay. Weir still thinks she's a hologram and summons up the hologram. It claims it was created in the image of the Morgan-Ascended creature, but the playback reveals Daniel is telling the truth. They check the power usage logs and determine no power was being used. The "hologram" apologizes.
The team initiates their plan and it triggers an energy exchange, but not. McKay suggests they use more bombs. They also have to get closer, which will mess up their sensors further. Teal'c detects the approaching Ori ship and they realize they're running out of time.
Morgan explains that over the thousands of years she's no longer Merlin's rival and they both Ascended. Now she believes the Ori pose too great a threat and is willing to help the humans and support Merlin. The Ori ship is unaware of Teal'c's presence and he extends his ship's cloak to include the stargate.
Morgan explains she had hoped her covert actions would have fooled her fellow Ascended as the humans would have seemingly got their answers on their own. Daniel demands that they give him clear answers and the Ascended are just as vested in the outcome as the humans are. Morgan is impressed by Daniel's speech and he figures she's afraid of being punished.
Teal'c gets the transmission from SGC warning the Odyssey of the approaching Wraith ship. The Odyssey is ready to launch their last two bombs when the Wraith ship appears. Teal'c contacts them warn of the Wraith's approach but they can't confirm with sensors due to their proximity to the black hole. They move away and the Wraith fire on them, knocking out the hyper drive. Sam suggests they get the Wraith to follow them into the black hole's horizon and beam their warheads on board, using the energy to trigger the wormhole.
Morgan tells them they have their answers, but when she tries to tell them something about the two planets and Merlin's weapon, she is pulled away.
Sam warns Teal'c to get his hyper drive on-line and get the heck out of there. He leaves and lures the Ori warship after him, while they beam the warheads aboard the Wraith ship and destroy it. The energy release forms the wormhole and destroys the Ori warship, and the stargate survives the explosion. They now have a permanent wormhole opened up via the black hole to the supergate.
Vala tries to reassure Daniel concerning Morgan's fate without much success. Daniel concludes that the Ascended won't be helping them, and they're on their own.