John nods, and runs up behind a piece of rumble so that his party can no longer see him. "I'm still here," he calls, once he's behind, "so don't worry about me!"

With that, he runs up the alley silently and invisible to any manner of creature with a brain, occasionally becoming visible for a second to take out a batch of headcrabs with blue shockwaves. They don't even have the chance to stalk him before they're thrown backwards with that blood-curdling cry.