"This madness of ours. It does. You see, Jerry Wolfe was nearly blinded in India when a Tower musket was discharged athwart his eyes. The bandages were removed as he was coming home, and he found he could see ... could see rather more than most of us can."
"Yes, sir," said the dignified voice. "May I ask what he could see, sir?"
"He could see into Hell," said Alec Talbot quietly.
"He could see that certain people are not—people," I went on. "Let me try to explain that. He discovered that there are among us many aliens of another race, perhaps from another dimension, or from another planet, or—who knows? He thought they were out of a different dimension, because he could see silvery lines behind them which he believed to be that dimension's scenery, as it were. Each of these aliens, these usurpers, as he called them, had stolen a human body, and was using it as a focal point of entrance into our world. Do you follow me?"
"With some difficulty, sir."
"Drop the 'sir', Johnson. We're all plain human beings together in this."
"Yes, sir."
"Well, he could see these alien creatures, but within them, or behind them, he could also see the human bodies they were occupying; the bodies which to everyone else appeared to be quite normal men and women. The bodies apparently didn't contain a human soul or mind or whatever you want to call it, but were only puppets for the interlopers. He sat in Charing Cross Station and made notes on them, at one stage of his adventures, and he decided that they were entering this world by usurping the bodies of newly-born children, children of unions between two of them or between one of them and a regular human. See?"
"Vaguely, sir."