Sanctuary: On the run from the Smoking Man, Mulder and Scully go undercover in Kentucky, hoping the Beeson-Lymon case will lead them to information that will finally bring CSM down. Meanwhile, Alex Krycek slowly recovers from a gunshot wound with the help of an unlikely caregiver from whom he can hide nothing. CSM hatches a nefarious plot to draw Mulder and Scully out into the open. Help, and resolution, come from unlikely quarters.
This second volume contains part 3 of the Sanctuary series. You absolutely have to read them all in order so grab the first two parts here.
Bardsmaid managed to somewhat redeem Krycek in this one, bestowing some humanity on him without it feeling at all forced. By the time I got to this one I was all in and didn't even notice how long it was.
This includes the Sanctuary postscripts. As the sequel to Sanctuary was never completed, you may choose to end your journey here, but I strongly recommend that you keep going with Topaz.
BTW, I may have gotten confused with which tags belong on which volumes. I just recently re-read them all in one huge binge and can't remember what happened when...