Battlestar Galactica Four Episode 17

Warning: Spoilers galore if you haven't seen No Exit, the fifth episode of the second half of Battlestar Galactica's fourth and final season.

"I don't want to be human. I want to see gamma rays, and I want to hear X-rays and I want to smell dark matter ... "

With shows like Battlestar, you expect things to move forward with every episode. To be given a new clue, let into the odd secret - to have something to mull over at the virtual water cooler. But rarely does TV offer up the torrent of new information we were handed last night.

Maybe they're trying to replicate the Cylon download experience for us. It was like the writers walked into the BSG top-secret spoilers vault, had a look at everything in storage, realised there wasn't going to be enough time for all of it, and thought, "Ah, frak it - here you go!".

What an opening. With the series heading towards its finale, it's a great time to indulge in a little nostalgia - and giving us a greatest hits of all the recap titles worked a treat:

THIS HAS ALL HAPPENED BEFORE (boom)
AND IT WILL HAPPEN AGAIN (yup, there's that bummer of a burnt-out Earth)
THE CYLONS WERE CREATED BY MAN (old-school Centurion alert!)
THEY REBELLED (Centurions with guns)
THEN THEY VANISHED (boom)
FORTY YEARS LATER (boom)
THEY CAME BACK (uh-oh, it's the Vipers ... )
THEY EVOLVED (hello Six)
50,298 HUMAN SURVIVORS (well, not after last week's mutiny there aren't)
HUNTED BY THE CYLONS (more explosions in the sky)
ELEVEN MODELS ARE KNOWN (yes, and some of them really do look like models - but will we ever get used to seeing Tigh, Tory, Tyrol and Anders in this lineup?)
ONE WAS SACRIFICED (It's Ellen: "I could use a drink ... You've always been there for me when I need you ... I'd do it all again.")

Cue some Matrix-style blood-red data zooming through the universe, and our first insight into what it might be like to download. Ellen, gasping for air in the Resurrection Hub hot tub, screaming at the sight of a Centurion standing guard in the room – then pulling herself together, slicking her hair back, and motioning politely, as if talking to a butler in a health spa: "Will you help me up please? It's OK, you can do that much." (The "thank you, you're very kind" as the centurion's metallic claws retract let us know that her memories of a life before "Ellen Tigh" really have returned.)

So let's try and get this straight. Not only is Ellen the final Cylon of the Final Five, she was resurrected 18 months ago (before the last Resurrection Hub got blown up), has been hanging out with Cavil and Boomer all this time - and she's actually the uber-Cylon who dreamt it all up in the first place. Busy lady.

Back on the Galactica, Anders was also taking a trip down memory lane - with the "word-salad" of his ancient past falling out of his mouth like a ranting Hybrid: "I'm on bright stars, I'm lost ... all the forgotten faces ... we seek the forgotten language ... "

As he pulled it together though, some actual facts emerged: the Final Five used to work on a research facility together (great moment with Chief and Tory pulling "yuck" faces like grossed-out primary school kids when Anders told them they used to be a couple). They all re-invented resurrection - or "organic memory transfer" - which originally came from Kobol, along with the 13th tribe. They wanted to find the other tribes and warn them to treat the Cylons well, but when they got to Caprica they were already at war. So they made a deal with the Centurions (THEN THEY VANISHED - ah, so that's what they were doing) and helped to develop the eight human bodies.

Of course, there are five episodes to go, and we couldn't have Anders give everything away. So, with a poignant "oh wow, everybody's glowing ... " Anders shut down.

Over on the Baseship we learned even more. Cavil and Ellen played out a Cylon morality play in front of Boomer, wrestling with the weight of vengeance, murder, justice and love.

Cavil's speech echoed Rutger Hauer's "I've seen things you people wouldn't believe" monologue in Blade Runner: "I saw a star explode and send out the building blocks of the universe ... And you know how I perceived one of the most glorious events in the universe? With these ridiculous gelatinous orbs in my skull."

Dean Stockwell seemed to be relishing the chance to chomp through Cavil's lines this week - "Sleep: it's a good example of a supremely unproductive human attribute that for some reason you chose to write into our software. Fortunately I was able to delete that particular sub-routine, and I stopped sleeping ... about 20 years ago"

What would Freud make of these guys? A scientist who created artificial life in her father's image that she then had a fling with ... Who still loves her Pinocchio-like son even though he took her memories away from her, used her for his own sexual gratification and now wants to rip open her head and have a look inside. It's all several notches up from "Luke, I am your father" for confused family politics - and yet, with typical BSG nonchalance, the revelations are chucked out along the way as we storm through the episode. What's next?

• Frak-watch and other Sitrep notes

"Get the frakking brain guy!" Starbuck makes a medical decision.

"You're frakking telling me they cut corners?" Adama slips in another reference to the show's early budget problems.

How's Ellen going to take Saul's Cylon-on-Cylon love-fest with Caprica Six?

Who is Daniel? The elusive Number Seven is another of the show's great unspoken mysteries that the mathematically aware of you will have noticed for some time. Is there one hidden in the fleet with his Cylon memories deleted like the rest? Or has his end really been "permanent"?

Why does Cavil hate being called "John" so much?

Chief offered Adama some Cylon resin to patch up the structural damage endemic in the Galactica's hull. How's that going to play out? Will it become a part-Cylon ship? Will Cavil be able to track it down? And have the Final Five been getting special Cylon induction courses to get them up to speed with all the benefits of toaster life?

We're down to 39,556 survivors after the mutiny's bloodbath.

There's some "equipment on the colony?" What colony? What equipment? What's Cavil talking about?

Who is the Cylon spy?

The Cylon revelations are crystallizing in "Battlestar Galactica" as the final one of the final five is unveiled, Anders becomes aware of the history of the final five on Earth, and the extent of Cavil's hate toward humanity is put on display.

The humans are going through their own evolutions as well. Bill Adama must struggle with the fact that his ship, a symbol of stability and safety among this ragtag fleet, is crumbling around him. Galen Tyrol shows him the damage, and is charged with fixing it. The other Adama, Lee, is given just as big a responsibility by President Roslin: basically to rebuild the government after Tom Zarek decided to scrap the last one (which I still believe was a wrong, out-of-character act for Zarek, despite his history of 20-plus years as a revolutionary who killed people, commenters!). Laura would remain as the president, but Lee would do the actual work.

To the Cylons on Galactica who are the cylons?...

Doc Cottle's excellently gruff beside manner is great, and before he lets the brain guy (guest star John Hodgman -- you know, PC from the commercials) get to the bullet in Anders' head, he lets Starbuck and the others speak to Sam. Anders' returning memories, which he gladly relays to the final four Cylons during storytelling time in the emergency room, fill in some of the reasons they're there, and tell of a benevolent purpose. They worked together on Earth in a research facility (Galen and Tori shacked up too) and helped reinvent "organic memory transfer." The people from Kobol had invented it first, but they rediscovered it.