I shouted. I thrust the end of my staff into the gravel and dragged it through, drawing a line in the dust and stones. I swiftly inscribed a quick, rough circle maybe four feet across around Murphy and me, actually getting between her gun and the grey suits for a second.“Dammit, Harry, get down!” she shouted.I did so, reaching out to touch the line in the gravel, slamming a quick effort of will into the simple design. Murphy’s gun barked twice. I felt the energy gather in the circle and coalesce in a rush, snapping into place in a sudden and invisible wall.The nearest of the grey suits staggered, and then flung itself into a forward dive. Murphy flinched back, and I grabbed her, hard, before she could cross the circle and disrupt it.The grey suit slammed into the circle as if striking a solid wall, rebounding from its surface in a flash of blue-white light that described a phantom cylinder in the air. An instant later, more of the grey suits did exactly the same thing, maybe twenty of them, each of them bouncing off the circle’s field.“Easy!”