Admiral Adama arrived at the door with blood on his hands. "I'm sorry, I don't think you want me to shake," actor Edward James Olmos said, presenting his red palms. With his world-weary eyes and the stained cuffs of his military coat, he looked like some battlefield surgeon fresh from triage.

Inside his dressing-room trailer, the star of the relentlessly bleak "Battlestar Galactica" washed his hands and apologized again. "And I can't tell you why I look like this." Olmos had just walked off the set of "Battlestar," which begins its fourth season on the Sci Fi Channel Friday night. More importantly, it's also the final season, and its creators have zealously guarded the plot twists.

"I can't even tell you whose blood it is," Olmos said with a wink, beginning to enjoy the fun. It's unusual to see Olmos smile when he's in his William Adama role: He's a sort of Churchill-in-space, trying to rally his people in the face of tremendous casualties and despair and also lead them on a quest for a fabled lost colony called Earth. Their struggle, for better or worse, is almost over. There are only 20 more episodes to sort out who will live, who will die and who will be outed as sleeper agents of the Cylons, the synthetic race that was created by humans and now aspires to push them out of existence.

Under slate-gray Canadian skies late last year, the cast of one of the most admired (and, according to the cruel math of ratings, one of the most undervalued) shows on television seemed to be mentally exhausted, anxious and sad. That's understandable given the show's looming end. They've lived through the annihilation of humanity for five years, but that doesn't make it any easier to say goodbye.

"It is difficult to move on, but it is the correct time, the natural pace of the story -- there's the beginning, the middle, and now it's time for the end," Olmos said. "We have hit so many notes, and now it's time to tie everything up."

Olmos has the wounded stare, craggy features and broad shoulders that look most comfortable in a posture of grief -- he has the ideal profile for "Battlestar," which presents a human civilization reduced to under 50,000 souls and a fleet of spaceships on the run. The lead ship is the Galactica, which like its leader Adama, has been un-retired in desperation after a sneak attack by the Cylons. That's the story arc, but the show's great distinctions are its wonderfully flawed characters and the religious, social and political questions that float by as they swim in the show's dire straits. Early on, series executive producer Ronald D. Moore wrote a mission statement for the planned "Galactica" series that pledged to break the standard sci-fi space-opera model and strive for a near-documentary texture, a sophisticated ambiguity to the stories and plenty of complications that the audience would recognize from the real world. Think you have unshakable opinions on the nature of suicide bombers, terrorism and torture? Try watching them tested in an alien atmosphere.

"The show is a dark mirror," Olmos said. "So, so dark. I was talking to one of the executives on the show recently and this person told me that they would never do something like this again, this kind of material. I have been doing this a long time, working in television, film, the theater, and this is the best material I've ever worked on in my life."

Others agree. It won a 2005 Peabody Award, the same year Time magazine named it the best show on television. It's picked up an Emmy, a Hugo and a shelf full of Saturn Awards as well. But it is also a very expensive series to mount, and as Jamie Bamber, who portrays Lee "Apollo" Adama, the son of the Galactica's leader, points out: "People who watch it say they love it. People who don't watch it say they've heard great things and they should watch it. The show is a success, but not as big a hit as people think, not in the commercial sense."

Many of the younger cast members such as Bamber and Tahmoh Penikett, who portrays Karl "Helo" Agathon, seem ready to shed their Galactica flight suits, pack up the industry credibility earned by their work on "Battlestar" and use it in places where they will be seen more.

"The end is in sight, for better or worse," said the London-born Bamber. "Every time I come to Vancouver now there will be a sort of Proustian element and a Pavlovian response. I'll think of my children being very young here, this stage and set, coming to North America, the sights and sounds. It will all be 'Battlestar.' "

Penikett was less sentimental: "There is a lot of television out there, and a lot of it is bad, but still it feels like time to head toward the horizon."

Olmos knows that feeling; he was a scene-stealing supporting character in the 1980s on "Miami Vice," and he's familiar with the stirring sensation that it's time to seek the next role, the next big show. But he said the stars, producers and writers may find that they miss "Battlestar" even more later. "The people involved don't know how special it is," he said. "In 20 years, I think they will look back and realize what it was."

The secret society

AS a journalist, it's odd to visit a television show in production where a publicist literally jumps up to cover your eyes with her hand whenever you go near the set. "Sorry! You can't look in here! Here, come this way . . . be careful, don't trip." The blindfold treatment is understandable: "Battlestar" fans include a zealous sect of sci-fi devotees who spend hours and hours analyzing every nuance and will send any spoiler or rumor pinging across the globe.

"The fans take it very seriously, which is nice," Penikett said. "A lot of the hard-core fans, I have to say, don't get out too much. And they're lacking certain social graces."

It was in deference to sci-fi genre fans that the show has the "Battlestar" moniker, which gave it instant name recognition with the crowd that dresses up like wookies or wear Spock ears at conventions. The first series called "Battlestar Galactica" was a show by Glen A. Larson, who had a career habit of creating successful but fairly derivative shows. His "B.J. and the Bear" was a lot like "Every Which Way But Loose," for instance, while "Alias Smith and Jones" was slagged as a rip-off of " Butch Cassidy and the Sundance Kid," and "The Fall Guy" reminded everyone of "Hooper." His "Galactica" premiered in 1978, a year after "Star Wars" created a cultural sensation, and it's mainly remembered in the popular mind for featuring Lorne Greene, a fuzzy robot dog and slow, shiny Cylons who appeared to be playing Pong with their red-dot eyes. With that legacy, Olmos didn't exactly jump at the pitch to revive the franchise.

"To me, it was 'Star Trek' and 'Star Wars,' so it was a knockoff of a knockoff. And so this new idea was going to be a remake of a knockoff of a knockoff? But then I read the script. This was in 2003, and it was completely informed by 9/11."

The modern show is to the original as "Lost" is to "Gilligan's Island." It has a dense web of a story and a huge cast of characters that make it a challenge for anyone late to the game. Another cast member, Tricia Helfer, who plays Cylon No. Six, describes "Battlestar" like an English Lit major who is worried about the final.

"I feel like I need to study more when I talk to the fans, the questions and comments they have. This show is on the pulse of what is going on in our society. It's not for couch potatoes flipping through the channels. If you're not engaged, you get lost."