saboteur

Over the course of a convincingly dreary London winter, a love triangle forms, with David in the role of underminer and saboteur.

But this much I can say: the catastrophic results of that man's actions could not have been worse if he had been a saboteur.

If a worker is badly paid and returns bad work for bad pay, he is a saboteur.

In other words, the saboteur abandons mass action in favor of ineffective and futile assaults upon men or property.

"The saboteur—seven men that I believe to be saboteurs—are aboard Hot Rod," the captain told him crisply.

I wonder what kind of a court martial they give a hero who turns out to be a saboteur.