There be spoilers here for anyone who hasn't watched the most recent episode of BSG, so if that's you, and if you don't want to know anything about this, then stop reading now. I imagine the length will prevent most people from reading it anyway, but I'm posting nonetheless.
I just finished watching the most recent BSG episode again to pay more attention to things I may not have noticed. I learned very early that this was necessary if I truly wanted to understand the plot. The writers and producers of this show have created an intricate masterpiece of televised fiction where almost no plot point or incident is simply a throwaway event. The revelation of the fifth cylon of the final five is a case in point. I'm not saying they set all this up in the beginning as I'm pretty sure they had to come to a later decision about who the final five were. But early in the series, the producers knew, basically, where they wanted to go, so they purposefully set up several possibilities, both to keep people guessing and to provide themselves with alternatives.
I noted the other day after the show aired that I knew a couple of people who had arrived at a theory that it was Ellen Tigh over a year ago. (In fact, it went back farther than that.) I was asked how that could be possible. It seems so out of left field. I did not answer at the time because I could not without providing spoilers, and the thread itself was marked as a "no spoiler" thread.
In the days since, as fans have talked about the show, many have said that there will be much explaining to do about how this is even possible, while others are irritated that the creators made her the final of the five because nothing that had happened in the past could have led to that conclusion. This is wrong. One thing BSG has done well in the past is to provide clues to its mysteries such that once the mystery is revealed, it maintains continuity. There are no unfair "tricks" to plot points.
Ellen Tigh as a cylon is no exception. This was offered as a distinct possibility all the way back in
Season One. All of us who have watched the show that long saw it. Many talked about it. It was a brief, but major deal that most of us subsequently ignored while we focused on all the major characters. Remember, at this time, we were at the point where anyone could have been a cylon, and Baltar's "test" for it had just been developed. The question about Ellen loomed and was front-and-center for a time, but it was never truly answered, and we forgot about it entirely after she died on New Caprica.
Here's the basis for her being the final of the Five. This all was used by the two people I saw who came up with the idea, in addition to some logic derived from the "Last Supper" picture (space empty next to Colonel Tigh and the information that the final cylon wasn't actually in the picture, but that it was a clue), but I've augmented it a bit with what we know now.
In Season 1, Episode 9 (Tigh Me Up, Tigh Me Down) we were first introduced to Ellen Tigh, Colonel Tigh's wife. Early in the episode we learn that Baltar's "cylon detector" is supposedly fully functional (earlier versions weren't "perfected"), and testing begins on people in "sensitive" positions as a top priority. This, of course, would include Commander Adama, and the President was quite curious to see the results of his test. (Notably, it would eventually probably include Saul as well, but that never happens on screen that I remember.)
However, Adama leaves the ship unannounced. This concerns Roslin and freaks out Tigh who finds himself in the position of having to deal with the sudden appearance of a cylon raider. The raider is acting erratically, which everyone finds curious, but no one can really explain, and they finally damage the thing causing it to jump out. (Deleted scenes shouldn't count toward this, but I'll mention one anyway. In a deleted scene the colonials detect an energy burst that some interpret as a possible communication between the raider and cylons in hiding in the fleet since they couldn't determine what ship it came from, implying it could have been two-way communication between the raider and other fleet ships. This is condensed to a single comment about some signal from it, and they didn't know what it meant.)
Adama eventually returns, bringing with him Ellen Tigh. Meanwhile, as Roslin learns while speaking with Baltar via the comms system, that Adama has canceled his test and provided a blood sample from another person who has a higher priority. That person's name is "Ellen." Roslin orders Baltar to resume testing Adama's sample immediately.
Just as Saul and Ellen are getting reacquainted and agree to "start over" (a phrase they repeat several times), Roslin calls Saul to her office to reveal her suspicions about Adama, questioning his suddenly leaving the ship just as the raider appeared. Tigh knocks her off her pedestal and reveals to her that he knew exactly where Adama was (he didn't know at the time actually), getting his wife. Roslin then calls Baltar and orders him to resume the test on "Ellen."
Later, at dinner, we all get to see Ellen in action and find out part of the reason Saul Tigh is drunk all the time. His wife constantly flirts with everyone, is apparently a lush of vast proportions, and is generally an embarrassment to him in public settings. But she starts off the dinner about as normal as she gets. There are many questions about her. Where has she been? What has she been doing? How did she manage to get aboard the Rising Star with no one noticing, and why can no one remember treating her during her supposed three weeks of being unconscious? She brushes off the questions in a drunken outpouring, and people generally chalk it up to Ellen being Ellen, everyone except Lee Adama who actually suggests after she is gone that she could be a cylon. This all comes across as something of a joke, especially when he says "If she's not, then we're all in trouble."
Indeed.
During dinner they have this bit of dialog in which she expresses an interest in Earth and reveals she knows things she really shouldn't have known:
Ellen Tigh: So Bill, now the question on everyone's mind -- and, I do mean everyone -- is "Where's Earth?" and "When are we going to get there?"
Commander Adama: Yeah... that's classified information.
Ellen Tigh: Oh, there's that word again!
Colonel Tigh: Ellen, leave the man alone.
Ellen Tigh: Come on! If there aren't privileges to being an XO's wife, then what's the point? I mean, Bill, we're all family here, so come on!
Laura Roslin: The need for secrecy is paramount, Ellen. Oh, I'm sorry. Perhaps you don't know that the Cylons look like us now.
Ellen Tigh: Oh... that. Yes. Yes, I knew that.
Laura Roslin: It's recent news. Most people just found out a few days ago.
Ellen Tigh: (thinking) A thing like that would travel fast.
Commander Adama: Any one of us could be a Cylon.
(the entire table goes silent)
Ellen Tigh: BOO!
(everyone jumps in their seat, but Ellen and Saul start laughing)
While Saul and Ellen are on their way back to their quarters, they run into Baltar, and she introduces herself. Baltar returns the introduction, but Ellen lets him know she knows very well who he is. Six shows up in Baltar's head and seems curious about Ellen and Baltar's meeting. "Something here, isn't there?" she asks rhetorically. Baltar and Ellen have a hand clasp that goes on too long, and they remark to each other about it, her in her flirty way, him in his defensive way that can't seem to resist the flirt. Saul exclaims that he's watching Baltar. Six says as she fades away, "You should be watching her."
Saul and Ellen then have a bit of an argument in which he accuses her of lying about what had happened on the Rising Star, after she clearly lied about Bill Adama making moves on her while she was there. She screams she's going to prove that Bill was there.
Then Roslin, Baltar, and Bill have a comical argument about why Ellen's results are taking so long. Bill suggests Ellen could be a cylon but says the greater problem is her effect on Saul. Saul and Ellen show up. More comedy mixed with serious argument. Bill reveals he had visited her while she was unconscious to get the blood sample to test her.
The raider shows back up on a collision course with Galactica. Saul "had a hunch" and launched alert fighters that bring it down and save the ship. Bill and Saul talk briefly about Ellen and her effect on him, after which Bill compliments him on his actions. He talks about needing Saul because he makes good calls when he's needed, "... that, and we're friends. I need you Saul. I don't want anything to come between us, not even Ellen."
As for Baltar's test, we find out Ellen has passed, but the closing dialog reveals that Baltar has decided that everyone will pass the test. Baltar's primary concern is Baltar. We are left with the possibility he's not even really testing anymore, just going through the motions. He thinks that the "skinjobs" might be able to communicate with each other and that if starts revealing them, he'll be assassinated. He's not even sure if his test actually works properly. It did *seem* to reveal Boomer, but then the "red" result turned "green" so it could have been a false-positive or an indication that cylons could defeat the test in some way. He's also concerned that through the testing what he did that led to the nuking of the colonies will be revealed. Whatever the specifics, Baltar is taking no chances with his own life.
Six asks Baltar, "So, what did her test
really say?"
"I'll never tell."