the second shock: the thing works, and now you're free
The shocking discovery that the thing actually does seem to work. Does keep you Substance-free. It’s improbable and shocking.
Context
The scene's hinge, and the theme's deepest paradox: the unparsable, corny, cliché-ridden program actually works, and no one — not even decades-sober members — can explain how ("You ask the scary old guys How AA Works and they smile their chilly smiles and say Just Fine"). The mechanism turns out to be the surrender of self-trust: Blind Faith born "not of zealotry or even belief" but of the conviction that your own judgment is the very thing that destroyed you. The last clause is the whole doctrine — "now they’ve got you, and you’re free" — freedom defined as the relief of no longer having to steer by a will you can no longer trust.