As you know, from the main history Dr. Daniel Jackson stays on "Abdyos" to live with the native people. Even though the Stargate Program is closed down, there is still miliatry personal guarding the Gate.
Until one day the Gate suddenly activates and the military personal guarding the Gate, are killed by some strange "people" who came through the Stargate. Then the Stargate is given active commission again and Colonel O'Neill is for the second time pulled out of retirement.
O'Neill fights to bring Dr. Jackson back from Abdyos to help with the problem. When O'Neill goes back to Abdyos he finds that the Goa'uld have returned to Abdyos, led by Apohisis, and they have taken many of the people - so that some of them can become new hosts to the Goa'uld.
Yet among the prisoners is Daniels' Abdydion wife, Shau'ri, who has been picked to be the new host to Apohisis' wife. With the knowledge of this Daniel swears to his wifes' father, that he will search for Shau'ri, and return with her.