Katherine runs to the museum, where she explains everything to Bevis in a rush. A Third Class apprentice overhears part of the discussion and realizes that Bevis and Katherine are the people who infiltrated the Guild of Engineers the night MEDUSA was tested. Katherine reveals her plan to attend a party at the guild hall with her father and sneak away to destroy MEDUSA. Bevis says she’ll need a bomb to destroy MEDUSA and offers to build her one. The eavesdropper runs to tell Crome Katherine’s plan.

Meanwhile, Valentine searches in vain for Katherine. He’s ashamed of the choices he made, but it’s too late to undo their effects. He knows Katherine’s right that Crome is doing terrible things and wishes that “he had the courage to stand up to Crome the way she wants him to” (316).

Bevis finishes building the bomb and fits it in a satchel so that Katherine can take it to the party. Shouts echo from somewhere in the museum, and the Engineer security team thunders up the stairs just as Bevis and Katherine step out onto the landing. They arrest Bevis and Katherine for conspiring to destroy MEDUSA. They’re taking Katherine to the party and sending Bevis back to the Deep Gut, making Bevis squeak with fear.