A high school senior gets inlisted by the CIA to defuse a nuclear bomb set for Washington DC, all before prom.

how's that?

Yeah, why would they call on a kid who can't possibly have the years of training and experience (or emotional maturity) that an adult pro would bring to the assignment?

(And internal threats are not legally within the purview of the CIA.)

I think your logline needs to connect the dots a little more. There are people trained to diffuse bombs, that's there job. You should give us a glimpse why the CIA enlisted this kid.