The Seventh Doctor takes Ace to a dying planet, Tarsus Six, about to be destroyed by a massive galactic shockwave. The population is piling into spacecrafts and trying to evacuate the planet before its inevitable destruction. As the Doctor and Ace roam about the last craft to leave Tarsus Six, Ace gets extremely annoyed at the fact that the Doctor won't tell her what their mission is. He eventually tells her that they're looking for an Ancient Artifact called the "Voice of Stone", but won't tell her why, or how, they have to find the thing in the middle of a terrifying natural disaster.
Ace meets the ship's officer, OhOne, and runs a Bavarian Fire Drill, pretending to be an Earth envoy. Since a quick scan reveals her to actually be from Earth (which is almost unheard of), she and the Doctor are allowed to run free on the ship. In doing so, Ace teleports a redheaded girl her own age into the ship out of compassion, not wanting to leave her behind on the dying planet. She's part of a cult which believes that the shockwave will cause everyone to Ascend to a Higher Plane of Existence. The girl, about Ace's own age, thanks her profusely before retreating into the ship.
The Doctor eventually finds the supposedly sacred Voice of Stone, which turns out to be a Time Lord hypercube message from the Eleventh Doctor. He tells Seven and Ace what the Plot Coupon of the day is: OhOne himself. Unfortunately, OhOne has realised that Ace is not an Earth envoy after all, and plans to incarcerate her. Even more unfortunately, OhOne also plans to make a Heroic Sacrifice in order to save his ship from destruction, since the redheaded girl plans to kill everyone for an Assimilation Plot. She ends up sacrificing her life instead, breaking Ace's heart but preserving OhOne for his future destiny.
Tropes
- Air-Vent Passageway: Ace and Ninejay escape capture by taking one.
- Alien Sky: Ace describes one with a purple sky and gem birds flying about.
- Always Save the Girl: For Ace, funnily enough.
- Apocalypse How: A Galactic class.
- Arc Symbol: The Doctor whispers, what we assume, is his name to the Hypercube, which shows up as a bit like a question mark, a motive that has been present with the Doctor since Tom Baker's last series to Sylvester McCoy's sweater.
- Ascend to a Higher Plane of Existence: The cult hopes to, by way of the shockwave.
- Assimilation Plot: What the cult has in mind.
- Big Dumb Object: The sun.
- Call-Back: Ace mentions Cybermen and Daleks.
- Call-Forward: The Voice of Stone is a Hypercube.
- Contemplate Our Navels: In the end, no one knows if the cult's ideas were true at all, though the Doctor comments on how infinite the probabilities of the universe are.
- Crisis of Faith: Ninejay has one when she realizes the Voice of Stone wasn't what she thought it was (it's actually a recording of a future Doctor).
- Cult: A good old-fashioned robes-and-chanting one.
- Dissonant Serenity: A Sender on board the Obscura sabotages the ship, dooming all the passengers to death. And explains her actions in a very calm manner.
- Doom Magnet: Ace says it's the other way around, really. Trouble is a good magnet for the Doctor.
- Fictional Colour: When the shockwave hits the Obscura, Ace sees colours that are normally not possible in this universe.
- Girl of the Week: In classic Doctor Who tradition, Ace gets one.
- Heroic Sacrifice: Captain OhOne tries to pull one off, before the Doctor realizes he has to live.
- If I Do Not Return
- Living Macguffin: OhOne.
- The Mole: There's a Sender devout on board the Obscura.
- More Expendable Than You: Ninejay pulls one on Ace.
- Mythology Gag:Ace: Others might have run, covered their faces, or cowered behind the sofa.
- Sand In My Eyes: After the Shockwave, Ace mentions trying to look at something, but her vision's gone blurry, and that she must have had something in her eyes.
- Space Station
- Surveillance Drone: A robotic bat flies around in the Obscura's vaults.
- The Power of Friendship: Ace's kindness ends up saving the day.
- The Tape Knew You Would Say That: Eleven neatly anticipates Ace's questions.
- Teleporters and Transporters: The Obscura has a transmat system on board.
- You Are Number 6: The humans all have numbers instead of names, though in an interesting subversion of the trope, it's not connected to any Dystopia.
- You Cannot Fight Fate: The Doctor says he and Ace can't save the colonies around the dying star. It's already happened.
