"Good evening, sir," you say very sweetly. "What brings you here at this late hour?" He stops in his tracks and gives you a conspiratorial glance. "I'm off to go take out the owner," he says. "He's been causing too much trouble for us around here. You in to help ol' Jimb?"
Attack Jimb. Go through with your job. Yell to warn Lou. You can go through with your job without attacking. Assist Jimb. Maybe the job wasn't so worthwhile. Tell Jimb you'll cover for him. If he doesn't want to kill Lou, he doesn't have to.