Dr. Cable is in the library, organizing the raid. Cable suspects Tally didn't do her infiltrating job very well, but Tally always has an answer. (That is, Tally always has a lie ready.)
Like: why did Tally try to escape the Specials? (That sounds like a terrible set-up for a joke.)
Because she didn't want to get in the way of their raid, obvs.
Also, Cable lets out that the pendant would call them if it was damaged. So when Tally threw it in the fire to destroy it because she decided to stay in the Smoke, that's when it called Special Circumstances to come destroy the Smoke. Oh, that's good irony.
Apparently, Dr. Cable thinks Tally called them on purpose—so Tally tells Cable that the pendant is hidden at the trading post.
Cable sends Tally and a Special out to go get it… after cuffing Tally's hands again, just for good measure.
At the trading post—where all the hoverboards are—Tally tricks the Special into cutting her plastic handcuffs and steals a hoverboard. (The section where she tricks the Special should be read by all good rebels, because it's a thing of beauty: first she makes up fake slang words and then she pretends to be clumsy. In other words, as a rebel, use your enemies' stereotypes of you against them.)