This is, perhaps, the worst time and place to ask Sonia to keep a secret. Drunk Sonia is an unfortunate combination of utter earnest and almost no impulse control, and so her desire to help Miles, to make sure she keeps his secret -- she's kept Byerly's after all, hasn't she? -- outweighs her better judgment by a long shot. And maybe even sober Sonia might have made the same decision.

Her eyes widen, because her mind fixates on the it would be kinder to kill me where I stand part, and so she doesn't think as much of the rest of it. But she does want to keep Miles's secret a secret, and if he wants to tell her, then surely there's a reason he wants her to know. She tries to shake her head and nod at the same time, managing some vaguely intelligible gesture, but her eyes are just as serious as ever.

"Of course. You have my word, Miles."