This is a planet-of-the-week episode, but contains elements that will later become part of the larger stargate mythos. We see the Nox for the first time, a race of beings with superior technology to the goa'uld, but who are a peaceful, enigmatic people. They are able to hide themselves and other things, to the point that even the goa'uld, who have been coming to the planet for over 400 years, do not know of their existence. They also have amazing healing powers, and can bring people back from death. The team go to their planet in search of a flying creature with the power of invisibility and run into their old pal Apophis and his small personal guard. It's the first time the show's primary antagonists have shown up since The enemy Within and despite seeming quite weak (only 3 jaffa following Apophis) they still manage to kill the human members of SG-1, who are then reanimated by the Nox.
In my mind, the Nox are one of the most cryptic groups of aliens to feature in the stargate world, as we never find much out about them other than that they're incredibly advanced compared to us. It's nice to see an advanced race of pacifists, too - often in science fiction, advanced races are shown either as aggressive towards us or as benefactors. The Nox, on the other hand, just want to be left alone.
Not much else happens in the episode - the dangers of 'meddling' with other cultures and the naïveté of children are shown - the Nox had gone undetected for hundreds of years before SG-1 visited their planet and started a fight (yes,
Han Teal'c shot first) and then because of a talk with Jack, the young nox Nafrayu confronts Apophis and is injured or killed (but returned to life by his fellows). At the end of the episode Jack repeats what the old nox told him - "The very young do not always do as they are told," referring to both Nafrayu and the human race.