On a chilly night in February 1894, Vastra, Strax, and Jenny Flint have been summoned to the Royal Observatory by William Christie. Last week, Christie found that some of the lenses in the recently refurbished large telescope had been scratched. He cleaned them, but the next day they were once again scratched. Christie explains that the only way someone could have messed up the telescope was if they were able to go inside it.
Strax whispers to Jenny that his internal comms unit has been picking up strange high-pitched chatter. Strax thinks that it's a whole battle fleet of Rutans.
Vastra tells Strax to be quiet and says that she has a suspicion on what's causing the problem. She tells Jenny to look into the telescope and focus on the scratches on the glass. Vastra explains that they are not scratches, but bite marks. She then declares that the culprits are with them in the room. She pulls a magnifying glass out of her purse and hands it to Strax and Jenny. They see thousands of small blue thumb-sized creatures.
Vastra explains that these are Gremlins, creatures that exist a millisecond out of the time of the planets they invade. In the last week, they discovered how to reach Earth's time and have began causing toothy trouble. The Gremlins begin breaking everything in the observatory. As parts of the roof start falling, Vastra tells Jenny to talk to the Gremlins.
In the morning, Christie thanks the Paternoster Gang for everything they've done. All the scratches have disappeared and Christie thinks he can see farther then before. Jenny thinks back to a few hours earlier. Vastra guided her through negotiations with the Gremlins. In return for fixing everything in the observatory, the Gremlins were guided by the Paternoster Gang to somewhere where they could eat junk to their hearts content: the bottom of the River Thames.
- Jenny says that Strax often thinks that Rutans are behind the crimes they investigate.
- This story was based on a real life attempted bombing of the Royal Observatory on 15 February 1894.