The Tenth Doctor and Donna respond to hundreds of distress calls coming from the planet Death's Deal. They're too late. In fact, they're so too late that a tourism industry has grown up around looking at the wreckage. They're quick tours though, because all the wildlife on Death's Deal is exceptionally unpleasant, and it's really not a good idea to stick around.
So naturally, the tour ship gets trashed and the TARDIS gets swallowed by a monster. That's when two of the tourists turn out to be pirates, Groogan and his not-girlfriend Lyric, looking for treasure. Together with the Doctor and Donna, and a molluscoid anthropologist called Krux, they set on a quest across the most deadly planet in the galaxy. And the Doctor's picked up another message. It just says "Alons-y!"
When they get to the treasure ship, there's no treasure, just Eleventh's message telling Tenth that he needs to save Erskine, and that the planet is full of Slaughter crystals. Donna and Krusk get seperated from the others, and have an adventure through the underground of the planet while the Doctor discovers that Erskine is a) the surveyor who wanted to declare the planet a site of environmental interest and was shot down by an evil mining corporation b) completely mad, calling himself Father of Paradise and sacrificing subsequent crash victims to the planet's nature gods, and c) Lyric's dad, and she was only hanging around with Groogan to try to find him. He also realises that slaughter crystals are an insanely powerful weapon, that the wildlife is being driven into a frenzy by the electromagnetic radation from all the distress calls, and that the evil mining cartel have been informed about the crystals and are on their way. Now he just has to deal with being sacrificed by Erskine.
- Asshole Victim: The disaster tourists. Especially Rude Woman Who's Actually Working For The Mining Corporation.
- Analogy Backfire: Donna does this to herself. When she's hurtling through an alien worm's digestive tract, protected by the shell of an alien mollusc, she tries to convince herself it's like the time she went zorbing. She hated zorbing.
- BBC Quarry: The original landing site is one.
- The Big Guy: Krux is an 8 foot tall, barnacle like humanoid with several tentacles instead of hands. And he's huge.
- Big "WHAT?!": Starting from a Flat "What.", as per the Doctor.
- Bioluminescence is Cool: See also Bizarre Alien Biology.
- Bizarre Alien Biology: Krusk has luminous tentacles that are part of his mating ritual, and can open up his shell and let Donna hide inside.
- Broken Bridge: Minutes into the story, a gigantic creature eats the TARDIS, trapping the Doctor and Donna on Death's Deal.
- Catch Phrase: The Doctor gets an "I'm sorry. I'm so sorry" and an "Alons-y!". The latter is also used by Eleventh as Something Only They Would Say.
- Call Back:
- The Doctor mentions having a friend who was a shapeshifter and an enemy who was a Master of disguise.
- The Eleventh Doctor comments on not being ginger, a reference to both his and Tenth's regeneration scenes.
- Death World: Death's Deal is "the most dangerous planet in the Galaxy!"
- Distress Call: Death's Deal is surrounded by them, both current and old, and the TARDIS receives them all.
- Everything Is Trying to Kill You: The planet's wildlife have all been enraged into unstoppable killers.
- Family-Unfriendly Death: Frimbs gets liquefied and eaten by a gigantic limpet.
- Giant Enemy Crab: Or at least crab-like legs. Eats a space pirate. Subverted with two crustaceans that Erskine has tamed.
- Hellish Copter: Well not exactly a helicopter, but a tour boat, but it blows up in a spectacular fashion.
- I Don't Like the Sound of That Place: Death's Deal.
- "I Know You're in There Somewhere" Fight: Lyric tries this on her father. The Doctor explains that at this point, remembering he was Merrit Erskine would just be too much for him to handle.
- I Want My Mommy:
- Memento Macguffin: Erskine has a locket containing pictures of his wife and daughter. He never opens it, because he doesn't want to be reminded.
- Nature Hero: Erskine, sort of.
- One-Hit Kill: One scratch from a Slaughter Crystal causes a lightning quick infection that first starts to sting, then takes away your senses and kills you under a minute.
- The Professor: Professor Erskin.
- She Is Not My Girlfriend: Lyric towards Groogan.
- Single-Biome Planet: The whole world seems to be one vast coral reef.
- Something Only They Would Say: The distress beacon from a ship called the Howling Jupiter beeps in Morse code. A-L-L-O-N-S—Y-. The Doctor deduces it must be a message for him.
- Space Pirates: Tag Groogan.
- The Tape Knew You Would Say That:
Eleventh Doctor: Or else millions upon millions will die.
Tenth Doctor: *through gritted teeth* But what must I do!?
Eleventh Doctor: And I know you're now asking "What must I do!?" because I know you best of all!
- Title Drop: Death's Deal is the name of the planet the story takes place on.
- Pet Monstrosity: Two crustaceans Erskine has tamed.
- Power Crystal: Slaughter crystals
- Prophecy Twist: Eleventh's message doesn't say which Erskine the Doctor needs to save.
- When She Smiles: Lyric smiles at the end of the story, for the first time.