Tris starts out the interrogation by declaring: "I think you're all idiots" (3.1). Tell us how you really feel, Tris.
In order to seem like less of a traitor, Tris lies and says that she was just following Marcus's orders, and she thought Marcus was working with Evelyn the whole time.
That's all it takes. Tris is off the hook. So are Christina and Cara.
As soon as she's free, Tris is ready to get the heck out of the city.
Uriah lets Tis know that Tobias wants to meet her later. We don't need a stethoscope to hear that heart skipping a beat.