“Abyss” is episode six of season six of Stargate SG-1.
After being infected with an unknown disease by what was presumably an Ancient in “Frozen”, Colonel O’Neill had a Tok’ra symbiote implanted to cure him. It was also hoped that the symbiote would be able to reveal some vital information. Once O’Neill was healed, and a new host found, it would then leave O’Neill.
That hasn’t happened yet, and O’Neill is captured by Ba’al, but the symbiote fled before the capture. O’Neill had also left without the Tok’ra’s knowledge. Ba’al wants information from O’Neill, but he claims not to have any knowledge of what happened. As a result, Ba’al is going to torture O’Neill to death – again and again. With a Goa’uld sarcophagus, you don’t really need to worry about whether someone will survive torture.
Daniel appears for the first time since he apparently Ascended in “Meridian”, although O’Neill thinks that he’s a delusion.