Fallen

Plot
The episode begins with Daniel found lying naked on an alien planet, and taken in by the locals. Meanwhile, at the SGC, Jonas Quinn discovers that the "lost city" that they have been searching for is a mistranslation; it is actually the "city of the lost." Furthermore, he points out that it would be the last on the list of Stargate addresses that Jack entered in the database when he had the repository of Ancient downloaded into his brain. SG-1 and another SG team go to that planet in hopes of finding the elusive city.

It turns out to be the same planet on which Daniel recently appeared. The team finds him and discovers that he has no memory of any of them. They talk with him several times, recounting past events, and finally convince him to come back with them to Earth. There Daniel deduces that Jonas had misinterpreted the tablet. In fact, the meaning is closer to “city lost to history.” Daniel hypothesizes that any references to the city have long since been removed from historical documents making it nearly impossible to locate. However, this leads to a plan to cripple Anubis' new super-weapon, which destroyed Abydos in Full Circle.

The team will plant a fake tablet for Anubis to find, claiming that the lost city is on that planet. Carter and O'Neill will pilot an F-302, equipped with hyperspace-burst capability, and penetrate the shields of Anubis' ship. In turn, this will allow them to fire missiles down a ventilation duct to the power core of the super-weapon. However, the Tok'ra have been unable to acquire the specifications of the ship, which are protected by codes written in Ancient. Daniel and Jonas will locate the vent from the interior of the ship. Meanwhile, Teal'c will be dispatched to the fleet of Yu, where he will alert Yu that Anubis' mothership can be compromised with the super-weapon disabled. O'Neill points out that the plan is the craziest they have ever concocted, and all involved agree. Nevertheless, they also all agree to participate.

An F-302 is taken through the gate to the planet, and a runway is built for it. Carter and O'Neill launch the F-302 and fly towards Anubis' ship on which Jonas and Daniel have already arrived by rings, having been implanted with radioactive Tok'ra isotopes in their blood to conceal them from sensors. They manage to reveal the location of the ventilation shaft while O'Neill and Carter barely evade a squadron of Death Gliders from the mothership. O'Neill and Carter then manage to destroy the power core without a hitch. Teal'c, with Yu's fleet, is arrested when Yu decides at the last minute to divert the fleet to another system, leaving Jonas and Daniel stranded on the ship. Cornered by Jaffa, Daniel escapes into a vent while Jonas is stunned with a Zat and captured. In the presence of Anubis, Jonas bravely defies the Goa’uld, adamantly saying he will reveal nothing, but Anubis calmly produces one of his mind probes.