After bringing back a mysterious orb from a huge temple on a desolate, uninhabitable planet, the team are flummoxed as to its purpose and workings, until something causes it to suddenly heat up very quickly. They take it to the gate room to try and send it back before anything happens, but it shoots out rods to attach itself to the floor and walls and, unfortunately, to Jack's shoulder. Weapons and cuttons tools have no effect and an organism starts spreading from the device through to Jack, the structure of the SGC, and the computer system.
Everybody races to try and save Jack and remove the device but nothing works. Eventually the infected computer system starts showing a strange glyph that appears on the orb itself and Daniel realises it's trying to communicate. They stop trying to hinder the organism and instead allow it to flourish, including in Jack's body, from which it speaks to them.
It turns out the orb was the last remaining part of a long-dead civilisation waiting for someone like SG-1 to come along and bring it somewhere it could reestablish itself. They come to a compromise to send the orb and its inhabitants to a primordial planet, so that both parties may survive.
This episode has no relation to anything else, but is pretty cool nonetheless. It features a completely alien race, and shows how badly things can go without communication. However, despite them clearly being a highly advanced race, it seems that after packing them off to a new homeworld, the SGC never has contact with them again, which is odd. They initially brought the orb back to Earth to study its power source, which could last an unimaginably long time, but upon relocating it they seem to lose all interest. Perhaps they decide the risk is too great, but as Teal'c points out to O'Neill, they must always take risks to try and find technology that will help defeat the goa'uld.
Teal'c remains a strong friend to Jack in this episode, barely leaving his side through the ordeal of being pinned to the wall and overtaken by microorganisms. He even tries comforting him by making a joke. Their already close relationship is strengthened a lot by what happens, and is shown by lots of close-up face shots of the two. Jack is Teal'c's closest Tau'ri friend, on what is an alien world without family or many of his friends from home.