“Key, front door please—­bell ring,” he explained tersely, taking the key from the table.

Miss Cornelia issued instructions.

“See that the chain is on the door, Billy.  Don’t open it all the way.  And get the visitor’s name before you let him in.”

She lowered her voice.

“If he says he is Mr. Anderson, let him in and take him to the library.”

Billy nodded and disappeared.  Dale turned to her aunt, the color out of her cheeks.

“Anderson?  Who is Mr.—­”

Miss Cornelia did not answer.  She thought for a moment.  Then she put her hand on Dale’s shoulder in a gesture of protective affection.

“Dale, dear—­you know how I love having you here—­but it might be better if you went back to the city.”

“Tonight, darling?” Dale managed a wan smile.  But Miss Cornelia seemed serious.

“There’s something behind all this disturbance—­something I don’t understand.  But I mean to.”

She glanced about to see if the Doctor was returning.  She lowered her voice.  She drew Dale closer to her.

“The man in the library is a detective from police headquarters,” she said.

She had expected Dale to show surprise—­excitement—­but the white mask of horror which the girl turned toward her appalled her.  The young body trembled under her hand for a moment like a leaf in the storm.

“Not—­the police!” breathed Dale in tones of utter consternation.  Miss Cornelia could not understand why the news had stirred her niece so deeply.  But there was no time to puzzle it out, she heard crunching steps on the terrace, the Doctor was returning.

“Ssh!” she whispered.  “It isn’t necessary to tell the Doctor.  I think he’s a sort of perambulating bedside gossip—­and once it’s known the police are here we’ll never catch the criminals!”

When the Doctor entered from the terrace, brushing drops of rain from his no longer immaculate evening clothes, Dale was back on her favorite settee and Miss Cornelia was poring over the mysterious missive that had been wrapped about the stone.

“He got away in the shrubbery,” said the Doctor disgustedly, taking out a handkerchief to fleck the spots of mud from his shoes.

Miss Cornelia gave him the letter of warning.  “Read this,” she said.

The Doctor adjusted a pair of pince-nez—­read the two crude sentences over—­once—­twice.  Then he looked shrewdly at Miss Cornelia.

“Were the others like this?” he queried.

She nodded.  “Practically.”

He hesitated for a moment like a man with an unpleasant social duty to face.

“Miss Van Gorder, may I speak frankly?”

“Generally speaking, I detest frankness,” said that lady grimly.  “But—­go on!”

The Doctor tapped the letter.  His face was wholly serious.

“I think you ought to leave this house,” he said bluntly.