I want a book about infiltrators

There’s a popular long-form piece going around now about a man who spent years infiltrating the upper echelons of American militias and right-wing groups.

I want a book about the protagonist who plays the loooong con like that, befriending the enemy to take them down from within, save the world from whatever the defined evil is. I’m not looking for a quick undercover case assignment and the political bent is negligible. Give me suspense about getting caught and possible moral compromise as they make friends with the baddies.

The Alice Network did this to a degree (in the WWI portion) without the moral compromise part. The protagonist worked for a women’s spy ring and had to get herself hired as a waitress in a restaurant owned by a French collaborator so she could eavesdrop on the German clientele. She had to assume a new identity and background and forget she knew a word of German so no one would suspect her. She had to give in to the advances of the proprietor so she didn’t get fired.

Honestly, I’d love a story where our infiltrator climbs the ranks to a position of power and shuts down the worst of it or cancels the space laser or something.