Sheppard, Ronon, Teyla, and McKay are being given a tour of a base on the planet Taranis. They are introduced to Chancellor Lycus who tells them that they are the first people that the Taranites have been able to contact with their Stargate. They have been trying to understand the ancient technology on their world but have made little progress. Rodney is volunteered by Sheppard to teach them how to use the technology and is escorted by Norina—an attractive scientist—to the generator room.
Chancellor Lycus guides the rest of the team through some tunnels to the main hanger. On the way a tremor rocks the base. The Chancellor leads them into the hanger which contains a giant ship.
Back on Atlantis, Sheppard tells Weir that the ship is similar to the Aurora. They are enthusiastic about the possibilities of using it to defend against the Wraith who are presumed to be on their way, but some repairs must be made before it is operational. Sheppard heads back to Taranis.
Rodney and Norina are working together on the generator that powers the Ancient shield, which would normally require a ZPM. She tells him that there is an enormous amount of heat beneath the surface and that she made some adjustments when the shield strength fluctuated recently. Some more warning lights lit up but she was unable to understand what they meant and shortly after that, the tremors began. Sheppard arrives to "establish relations" with the Taranites and offers her a break but Rodney refuses. He notices that the shields have been running for over a year. She tells him that when their long-range scanners detected a rise in Wraith activity they raised the shields and have left them up ever since. Rodney berates her that the shields are only for emergencies. He then notices that the reason the Ancients built the base where it is, is due to the fact that they are directly on top of an active super-volcano.
Dr. Weir negotiates with Chancellor Lycus in his office. She tries to get him to give them the ship but he is aware of its power and does not like the idea. She gets a message from Sheppard telling her that there is a problem; a sudden large tremor illustrates his point.
Rodney explains the situation to everyone in a meeting room on the base. This volcano is extremely large: the caldera is over 50 miles wide and a giant sea of molten rock is just beneath the surface. The Ancients built the base here to tap into the massive geothermal energy. Normally, there would be many thousand years between eruptions but because of the continuous use of the shields, the pressure of the magma chamber has increased beyond repair and is continuing to increase. Magma is pouring in directly beneath the base and there is no way to release the pressure. Sheppard suggests evacuating the Taranites from the area but Rodney explains that when this volcano erupts, all life on the entire planet will be eliminated and that they must evacuate to another planet. The Chancellor excuses himself and leaves.
Dr. Weir enters the Chancellor's office. She tries to convince him to evacuate but he is suspicious about the timing since as soon as they learned of the ship, they suggested that the Taranites evacuate the planet. More tremors occur around the volcano and Chancellor Lycus eventually accepts Weir's offer to evacuate people to Atlantis for now.
Evacuation procedures begin. Dr. Beckett tends to the wounded and Teyla and Ronon go to help Sheppard organize the evacuees, while Weir and the Chancellor head to Atlantis to handle the arrivals. The first group goes through the gate but as the second begins their escape, a massive tremor occurs. The refugees flee for cover and the ground around the gate opens up. Magma pours out and the gate falls into it.
The shield on the Atlantis gate goes up and protects them from large hits of energy that bombard the gate. The gate technician explains to Weir that he raised the shield by emergency command from Rodney. They try to dial the Taranis gate but cannot connect. The Chancellor becomes more suspicious, accusing her of staging the whole incident, but Weir explains that she did not and that they are both cut off from their people.
Rodney begins to panic because they are trapped on the volcano with no way to escape. Sheppard expects that the Daedalus will be coming for them but as a backup, he tells McKay to fix the ship in the hanger. McKay is upset about having to do everything and being expected to save everyone but uses it as a chance to impress Norina.
They examine the new ship. Rodney activates life support and finds the ship's name: "Hippaferelcus". Sheppard decides against that name. Rodney tries to suggest a new one, but Sheppard interrupts him and vetoes "Enterprise". They decide to name it later. They receive a signal from the Daedalus. They cannot be beamed out because that part of the base is shielded. Sheppard refuses to go outside to be evacuated because they cannot just abandon the Taranites. Unfortunately evacuating everyone on the planet would require four trips and the Daedalus is short on resources as it is. However, the tremors have stopped so they may be able to pull it off, but Rodney will still try to fix the new ship—which Sheppard names the Orion —as plan B.
Ronon and Teyla organize the Taranites for evacuation. The Daedalus beams up the first group and heads back to Atlantis. Dr. Zelenka notifies Dr. Weir that the long-range scanners have detected a single Wraith ship about three weeks away.
Norina tells Rodney that she has already learned a lot from him in just a few hours and that she would like to continue to work with him. Flustered, Rodney only manages to stammer. A tremor shakes the base and Rodney ducks under the console while Sheppard moves to protect Norina; Rodney gets flushed.
Teyla tells the next group of Taranites that they will be evacuated soon but some insist on heading for the sea on foot instead. Time is running out but Rodney has not yet gotten the ship's engines functional.
Dr. Beckett, Teyla, and Ronon try to convince the Taranites that heading for water is futile but some of them refuse wait any longer and head out anyway. Teyla gathers the rest and they head through the tunnels toward the hanger. The Chancellor and Dr. Weir ponder the fate of the Taranites and he apologizes to her for being suspicious.
Sheppard receives the Taranite refugees in the base and directs them to the hanger. Rodney warns him that toxic gas is venting into the atmosphere everywhere. Ronon has left to get the last family from the edge of the village but the gas is already starting to surround them.
When Sheppard returns to the ship, Rodney tells him that two fissures have opened near the base and a lava flow has emptied over the hanger doors. Even if McKay can fix the engines, they will not be able to get out because there is a massive quantity of lava right above them so they are trapped.
Ronon arrives with the last family but Teyla tells him that the tunnels back to the base have collapsed, they have lost communications, and the gas is continuing to seep in. Sheppard decides that they can blast the doors open with drones but Norina points out that the lava would pour in on them. Rodney gets an idea and investigates a terminal.
Ronon suggests heading for the base on foot outside but there is too much gas. Teyla thinks that they should stay inside where they can still breathe. Sheppard tries to radio them but cannot contact them. Teyla decides that they should have headed back on foot as Ronon suggested but Ronon agrees with her, that as long as they can breathe they still have hope. They are faint and the Taranite family with them is barely alive. They all begin to lose consciousness when just in time, they are beamed out.
Colonel Caldwell tells Weir that he does not know if Sheppard and the rest are alive or not because he cannot detect life signs. He criticizes Sheppard for endangering everyone by trying to save them all instead of taking the sure road and saving fewer.
Sheppard tries to bring the last group of villagers to the hanger but the doors in the tunnels are sealed and extremely hot. Rodney says that he will tell Norina to try to find them a path but then another tremor knocks out communications.
Hermiod attempts to calculate the remaining time until the main eruption. He offers that they should leave but Col. Caldwell does not consider that an option. Toxic gasses begin to seep into the tunnels so Sheppard tells the villagers to take shallow breaths as they try to make their way to the hanger.
Norina tries to contact Sheppard but cannot because of the electromagnetic energy in the atmosphere. McKay explains that the volcano is about to blow. Sheppard gets to a door which he pries open. Luckily this one leads into the hanger so he and the villagers board the Orion.
Rodney explains his plan. He could not fix the sub-light engines in the time left so instead he patched the power system to divert emergency power to the hyper-drive. He intends to raise the shields to full strength when the volcano erupts to protect them long enough to be ejected into the sky, at which point he will activate the hyper-drive for a moment to put them out into orbit. However, he does not expect it to work. Hermiod determines that the eruption will occur in 52 seconds.
Rodney bends his fingernail back and makes a big deal of it, to the ire of everyone else. He finishes up and they prepare to put his plan into motion. The volcano begins to shake and explosions begin outside. The ground beneath the hanger collapses causing the Orion to sink into the lava. From orbit we see an enormous explosion on the planet and moments later the Orion comes out of hyperspace just beyond the camera. The Daedalus hails the Orion and is happy to discover that everyone has been saved.
At a debriefing on Atlantis, Rodney says that a cloud of ash has covered the entire planet, so the Taranites cannot return for many years. Weir informs them that they have found a planet that the Taranites can go to and asks Sheppard and his team to assist them. Rodney and Sheppard bump heads again over Norina. Weir tells Rodney to fix the Orion as soon as possible because Chancellor Lycus has allowed them to use the ship as thanks for their help. Caldwell brings up the hive ship that is on the way. Thanks to the Orion, their supply of drones is replenished, but if more Hive ships come, it will still not be enough.