Adm. Helena Cain (Michelle Forbes) does the unthinkable in the war for humanity's survival.

Sci Fi photos Kendra Shaw (Stephanie Jacobsen), left, faces difficult choices as she works with Lee "Apollo" Adama (Jamie Bamber) and Kara "Starbuck" Thrace (Katee Sackhoff) in the "Battlestar Galactica" episode "Razor."

"Battlestar Galactica" has regained some of its original punch with "Razor," a two-hour special premiering at 9 tonight on Sci Fi.

"Razor" will remind fans of why they came to like "Galactica."

The series, a dark remake of the original show, has amazed viewers with its plot and character twists, and it has made powerful statements about war and humanity. Its story of human colonists trying to escape from or defeat an enemy has parallels to today's world crises. Specifically, "Galactica" has examined how far a government should go in the name of security, a question that faces the United States and other nations in today's post-9/11 world.

That's why "Galactica" fans should watch "Razor." The episode deals with the question of what happens to morality when survival seems uncertain. "Razor" makes it clear that the answer is complicated.

The morality question begins with what it means to be a Razor. The term refers to the best of the Viper pilots and Marines, and it's the kind of title that can only be earned during war. Razors do what they must without hesitation.

The episode goes back in time to Lee "Apollo" Adama's (Jamie Bamber) first mission as commander of the Battlestar Pegasus. Apollo has decided to make Kendra Shaw (the talented Stephanie Jacobsen) his executive officer because of her bold and rebellious nature. He needs a strong officer who isn't afraid to question him.

"Razor" then goes back further in time to show how Kendra evolved when she served under the Pegasus' original commander, Adm. Helena Cain (Michelle Forbes).

Cain does what she feels she must after the Cylons, a robotic species created by humans, destroy the 12 human colonies. Cain is aboard the Pegasus at the time, and she and her crew are unaware of the Battlestar Galactica. Are they all that's left of humanity?

As "Galactica" fans know from previous episodes, Cain does some horrible things, including executing innocent civilians, and "Razor" doesn't shy away from that. She's a villain for what she has done, but "Razor" examines why she did it.

Then "Razor" jumps back to Apollo's time to show what kind of warrior Kendra chooses to be.

The episode also includes some flashbacks to show a deadly danger that won't be spoiled here.

"Razor" succeeds where many of last season's episodes failed because writer Michael Taylor has proven something about "Battlestar Galactica." This series works a thousand times better when the plots drive the characters and not the reverse. Last season faltered badly when too much time was spent on personality conflicts and love affairs gone sour. The sexual tension between Kara "Starbuck" Thrace (Katee Sackhoff) and Apollo took viewers away from the plot.

With "Razor," "Galactica" is back on course. "Razor" is a promising revival of the series.

After tonight, fans will be eager to see the regular episodes for the fourth and final season, which is scheduled to begin in April.