In the begining of this episode Jack O'Neill gets hit with a spear leaving Captain Samantha Carter in charge of SG-1. Sg-1 is ordered by General Hammond to go to the planet that sent the spear thourgh the stargate to investigate what aliens were there and why they threw a spear thourgh the stargate. And mainly to figure out why SG-11 didn't return and rescue SG-11 if needed.
This episode was the first to really show Captain Carter's ability to lead. The show itself was average for a stargate show, which means it still was great but there were better episodes. And worse ones too.
This episode was nessisary for the develement of the series, if nothing else.