“Be careful what you say,” said Royce gruffly, “you’ll frighten Miss Armstrong.”

“I hope so,” said the man with the clear voice.

As the woman winced and everyone else wondered, he went on:  “I am somewhat used to Miss Armstrong’s tremors.  I have seen her trembling off and on for years.  And some said she was shaking with cold and some she was shaking with fear, but I know she was shaking with hate and wicked anger—­fiends that have had their feast this morning.  She would have been away by now with her lover and all the money but for me.  Ever since my poor old master prevented her from marrying that tipsy blackguard—­”

“Stop,” said Gilder very sternly.  “We have nothing to do with your family fancies or suspicions.  Unless you have some practical evidence, your mere opinions—­”

“Oh!  I’ll give you practical evidence,” cut in Magnus, in his hacking accent.  “You’ll have to subpoena me, Mr. Inspector, and I shall have to tell the truth.  And the truth is this:  An instant after the old man was pitched bleeding out of the window, I ran into the attic, and found his daughter swooning on the floor with a red dagger still in her hand.  Allow me to hand that also to the proper authorities.”  He took from his tail-pocket a long horn-hilted knife with a red smear on it, and handed it politely to the sergeant.  Then he stood back again, and his slits of eyes almost faded from his face in one fat Chinese sneer.

Merton felt an almost bodily sickness at the sight of him; and he muttered to Gilder:  “Surely you would take Miss Armstrong’s word against his?”

Father Brown suddenly lifted a face so absurdly fresh that it looked somehow as if he had just washed it.  “Yes,” he said, radiating innocence, “but is Miss Armstrong’s word against his?”

The girl uttered a startled, singular little cry; everyone looked at her.  Her figure was rigid as if paralysed; only her face within its frame of faint brown hair was alive with an appalling surprise.  She stood like one of a sudden lassooed and throttled.

“This man,” said Mr. Gilder gravely, “actually says that you were found grasping a knife, insensible, after the murder.”

“He says the truth,” answered Alice.

The next fact of which they were conscious was that Patrick Royce strode with his great stooping head into their ring and uttered the singular words:  “Well, if I’ve got to go, I’ll have a bit of pleasure first.”

His huge shoulder heaved and he sent an iron fist smash into Magnus’s bland Mongolian visage, laying him on the lawn as flat as a starfish.  Two or three of the police instantly put their hands on Royce; but to the rest it seemed as if all reason had broken up and the universe were turning into a brainless harlequinade.

“None of that, Mr. Royce,” Gilder had called out authoritatively.  “I shall arrest you for assault.”

“No, you won’t,” answered the secretary in a voice like an iron gong, “you will arrest me for murder.”