SG-1 is about to go on a mission to find a planet for the Enkarans when the 7th chevron doesn't lock, the problem turns out to be an energy spike caused by the second gate being active at the same time as the SGC was dialing out. The second gate is detected in Siberia, Russia where the Russians obviously found the second gate, which crashed in the Pacific Ocean in Nemesis. Because the USAF hasn't swept the whole Pacific Ocean, the Russians had found it.
SG-1 heads to Russia by plane where they have to jump out of a plane because it's too frozen down there. En route they are met by a Russian doctor named Dr. Markov who will take them to the Russian Stargate Center, which was an old power station.
When they arrive they find that the stargate is stuck on and drawing energy from the contacted planet (Like the black hole incident which she knew about) The Russians would use precise timing to prevent the SGC from knowing about it, the gate is dialed to a planet completely underwater (The 8th planet they planned to go to), They had the real Earth DHD which was confiscated by the Germans in WW2 from Giza. The last sub brought back a sample of the water but as it returned to Earth it experienced difficulty getting through, but the doctor thought it was something designed to keep water from entering the gate. The water had amazing properties, it generates heat just a few degrees above room temperature.
In the gate room they find scientists and some personnel dead, they had shot the scientists. The Russians already sent a drone through and it may be the reason the gate is still on - it is and they couldn't just wait for it to run out of power because it was nuclear powered which would last for an estimated 10 Years (it's nuclear powered because they thought of leaving them there for further research) so Carter, Daniel and Dr. Markov go through to get the drone and de-activate it.
After they succeed in de-activating the drone the gate shuts off. O'Neill and Teal'c take a look around and find Colonel Maybourne frozen in a freezer - they put him on a table and a few moments later he wakes up and starts walking forward and barfed out some watery substance.
The water enters Teal'c who then dials to the planet and coughs out the substance. Meanwhile, in the sub, the engines burn out because of some resistance. It turns out that Col. Maybourne is the reason the Russians learned to use the gate so quickly. He explains that the dead personnel are because the water got inside them - the water in Maybourne took him in the freezer to keep him (and the water) alive.
Markov fixes the engines but they still can't move because the pressure in the water is rising all of a sudden - the glass cracks and then the whole window cracks but the water doesn't rush in, it just stays outside. Daniel touches it but then it sucks him in and then the Doctor and Carter.
On Earth the gate activates and Sam, Daniel and the doctor are returned to the base in Russia and the water at the base returns to its homeworld.