Lin Tan gets into the plan storage room, with the aim of finding out whether this odd girder arrangement was there from the start or added later. She passes herself as being on an errand, but the filing system defeats her; she’s able to confirm that there are several plans with the odd arrangement, and doesn’t see any without, but she’s not able to say for certain that it was there at the beginning.

Bessie fakes an illness to get back to the village, posts the note, and picks up some cardboard from the post office; there’s also a letter from St John for Millie. He confirms that it’s filtering and separating magic, and says that it’s not in the style of any magical tradition he knows. Bessie builds a collapsible model, with three frames and struts between them; it has an immediate luck-separating effect.

Millie manages to brush past Squadron Leader Rope, the “assistant design” who’s done much of the world, and finds that he’s thinking of the R101 as a lucky ship. While he’s away, Lin Tan looks in his office; the only things visible with magic, to a cursory inspection, are a wire model of the extension (just two cross-frames) and a pipe-rack, the latter very much less magical.

When work ends, with the test flight tomorrow, there’s an informal party for the staff. (They’re told there’ll be no work tomorrow, though spectators are welcome.) Millie brushes against several of the engineers, and against Rope again; he’s thinking about frame stress, and the luckiness of the ship. When Gertrude prompts him with this, he says that the R101 has “got it in her bones”, and thinks that “as long as the frames hold it’ll all be fine”.

Millie tries to sneak aboard to get another look at the central concentration, but she’s turned back by a watchman. Gertrude tries to make mental contact from a distance; she’s not certain, as it’s quite far away, but she thinks it has no mind.

Millie walks back to the village and manages to get St John on the phone, to explain the situation. Given Rope’s thoughts, they wonder about the effects of distorting the frame; he says “hold on a moment”, and at the other end of the phone there’s a creaking noise followed by a burst of ignition and “my word”. When he loaded down his wooden model and bent it out of shape, it caught fire.

Once everyone’s back at the house, they make some more experiments: tracing the frame shape on a pleated piece of paper, so that it can be broken by unfolding it, and making a deliberately deformable model. They leave these for a bit to let them build up some charge; after supper, unfolding the paper leaves it ripped into three pieces along the folds. Pushing on the model (Molly’s prepared to say just what a reasonable engineering limit would be) leaves it intact; it’s only when it’s pushed quite a bit further, not actually to the point of breaking but to the extent that even without consideration of magic the ship would need significant repairs before being considered airworthy again, that all the joints collapse and the model falls apart.