The Beast attempts to split up the team by preying on their fears and regrest. Rose is told that she will die in battle in the near future (End of season 3?)

The Doctor abseils into the Pit and when the line runs out, drops the line and jumps the rest of the way into the darkness. (He'd done this before in Planet of Evil but since that nasty fall in Logopolis he hasn't really been into falling anywhere!)

The security guard dies helping the team escape via a ventilation shaft-like access tunnel. The team get to Ood central and broadcast a brainstorm to knock the Ood out. They succeed but they have to leave the base.

The captain orders that they leave via the rocket and they drug Rose to get her to come with them.

The Doctor wakes up at the bottom of the pit and meets the beast which is bigger than King Kong and wider than Godzilla. A massive creature, but with no intelligence. The Doctor realises that the intelligence has escaped and we cross to the possessed Toby in the rocket covered in 'before this universe' symbols.

 Excellent, excellent, excellent. 10 out of 10.

I was a bit disappointed by the Doctor's admission that he didn't believe that the beast was before this universe. Doesn't he remember the creature in Terminus that jump-started this universe from the one before?

Otherwise this is definitely the story to show potential fans interested in a serious science fiction story akin to Alien, with a bit of Event Horizon for good measure.

Here's the BBC blurb:
"Rose battles the murderous Ood and the Doctor finds his every belief being challenged to the core, as the Pit beckons in the concluding part of this two-part story.

With the planet threatening to fall into the Black Hole, the Doctor must make the ultimate sacrifice – but can he save the entire universe from the Beast?"

David Tennant plays the Doctor, Billie Piper plays Rose and Will Thorp plays Toby. 
Trivia: Love the reference to Demos re: The Daemons