There is only one Forsaken left whose whereabouts have not been even vaguely identified.
We know (or think we do) that:
CLUE #1: Demandred, Semirhage, and Mesaana work together. This we know from Lord of Chaos. Mesaana is known to be in the White Tower. Demandred is, we suspect, in the Black Tower. Logic suggests that Semirhage, wherever she is, will also be in command of a major channeling/military force. There are only two such forces left - Salidar and the Seanchan. Obviously, Semirhage is not in charge of Salidar; Egwene is. (Halima/Aran'gar/Balthameal is trying to worm her way into dealing with that, however.) Hence, it is my opinion that Semirhage is with the Seanchan invasion.
CLUE #2: The tension between the Seanchan, the Asha'man and the Aes Sedai would fit with the assertion that Demandred, Semirhage, and Mesaana all undercut each other, yet were never separable.
CLUE #3: Semirhage, we know, has a "willful charge." Who could this be? I submit that one possibility is the High Lady Suroth, leader of the Seanchan Hailene and a definitely willful person. Suroth, a known Darkfriend, seems to have a direct line to all sorts of information that she shouldn't have (the name Asha'man; knowledge that Traveling has been rediscovered, exact numbers, etc). This information could only have been hers through Darkfriend relays to the other side (i.e. Taimandred's cronies). I submit this is Suroth's Voice, Alwhin (a known channeler - at least, known to us; to the Seanchan, she's just a sul'dam.) This would explain why Liandrin and another woman recognizable as failed Black Ajah would show up under Suroth.
CLUE #4: "Demandred liked using proxies." Suroth, through Semirhage, is Demandred's proxy.
CLUE #5: Proximity to the Salidar Aes Sedai. I think it exceedingly likely that Semirhage is also Sheriam's torturer. Via Aran'gar, Semirhage can get the coordinates for the Salidar Aes Sedai camp and Travel or Skim there whenever. Popping out in a tent, she will not be noticed arriving. As for channeling, this is a camp filled with Aes Sedai; channeling will not be noticed. The modus operandi of Sheriam's torture (bound with the Power, immediately stripped using the Power, a "motherly" caress, the imitation of actual care, the condescending tone) absolutely scream Semirhage. (Compare with the torture of Cabriana Mecandes.) Therefore, Semirhage must be in a position where she must know about the Salidar Aes Sedai movements. Therefore, Semirhage is involved in a plot concerning the Aes Sedai. Add this to Clue #1, and it is certain that Semirhage is extracting information for the Mesaana/Demandred/Semirhage caucus to plan with. (Mesaana wouldn't do this herself; there's too much risk of being caught. Why not send the Numero Uno Information Extractor Extraordinaire to get your intelligence for you?)
CLUE #6: But why not just get the information from Aran'gar, who has about as much access and probably more chance to extract info from Egwene as Sheriam? Answer: Semirhage has no access to Aran'gar, who is working for Moridin, in a completely different conspiracy. More evidence that it is Semirhage that tortured Sheriam.
SUMMATION: It is my belief that Semirhage is riding with the Seanchan, either as Alwhin or as another member of Suroth's retinue. I believe that she is working with Demandred/Taim and Mesaana/Danelle to control and divide the various factions of channelers, with Mesaana in the White Tower, Demandred in the Black Tower, and Semirhage with the Seanchan. (Remember, Salidar did not exist until later, and was a possibly unintended side effect of a Black Ajah plot.) I also believe that, at Mesaana's request, Semirhage is performing extraction torture on Sheriam.
wotmania says: What you are saying makes a lot of sense. A lot of this theory fits together very well... Hopefully in Winter's Heart we will learn a bit more about Semirhage - all the Forsaken are interesting characters, and we have yet to learn much of anything about Semirhage.
Alwhin