Wait for them to pass. Have PW move silently up behind them and disable them with the knife. Stat where we are and fire on them with the revolver only if they manage to draw weapons.
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You wait, staying absolutely still, as the men walk past. As they pass the alley where piecewise is waiting, you order him to silently disable them. Piecewise moves from the alley in a sort of long legged lope, not quite running but not walking either. He closes the distance within a few moments, before any of the men can react to the small amount of sound he is making. Here, from the back, you can't quite make out exactly what happens. The skeleton moves in to the center of the group and you see metal flash. He strikes the head of the man to his left, then turns and strikes the man to the right. The man in the center, who he's directly behind, spins to see whats happening only to have a boney hand clamp onto his face and shove him to the ground. The other hand works quickly, like the needle of a sewing machine, thrusting down repeatedly, almost too rapidly to see.
After a moment Piecewise stands back up and steps a few feet away from the bodies. Despite the work he just undertook, he has a remarkably small amount of blood on him; just a few shining wet spots here and there on his coat from stray droplets. The men are all laying out on the street: the one on the left is completely still, while the one on the right is still spasmotic, the metal spike bayonet embedded in the back of his head. The one in the center though seems to be not quite dead, though clearly only seconds from it. It all took maybe 5 or 6 seconds.