She was still there when the door opened and Carlton came in. He had a highball in his hand, and his eyes were bloodshot. He seemed startled when he saw her.

“Sorry,” he said, backing out. “I didn’t know—I thought my mother was here.”

He was looking at her suspiciously. Hilda smiled, her small demure smile.

“She hasn’t come back, Mr. Fairbanks. I was installing a bell for her.”

“A bell? What for?”

“So if anything bothers her in the night she can ring it. I might not hear her call. Or she might not be able to.”

He had recovered, however.

“All damn nonsense, if you ask me,” he said, swaying slightly. “Who would want to bother her?”

“Or want to poison her, Mr. Fairbanks?”

He colored. The veins on his forehead swelled.

“We’ve only got young Brooke’s word for that. I don’t believe it.”

“He seems pretty positive.”

“Sure he does,” he said violently. “Look what he gets out of it! An important patient, grateful because he saved her life! If I had my way—”

He did not finish. He turned and left her, slamming the door behind him.

Hilda went downstairs. Ida was out, and Maggie was alone in the kitchen. She was drinking a cup of tea, and she eyed Hilda without expression.

“I want to try an experiment,” Hilda said. “Maybe you’ll help me. It’s about those raps you heard.”

“What about them? I heard them, no matter who says what.”

“Exactly. I’m sure you did. Only I think I know how they happened. If you’ll go up to Mrs. Fairbanks’s room—”

“I’m not going there alone,” said Maggie stolidly. Hilda was exasperated.

“Don’t be an idiot. It’s broad daylight, and anything you hear I’ll be doing. All I want to know is if the noise is the same.”

In the end an unwilling Maggie was installed in the room, but with the door open and giving every indication of immediate flight. The house was very quiet. Only a faint rumble of the traffic on Grove Avenue penetrated its thick walls, and Hilda, making her way to the basement on rubber-heeled shoes, might have been a small and dauntless ghost herself.

She found the furnace without difficulty. She could hardly have missed it. It stood Medusa-like in the center of a large room, with its huge hot-air pipes extending in every direction. She opened the door, and reaching inside rapped the iron wall of the firebox, at first softly, then louder. After that she tried the pipes but, as they were covered with asbestos, with less hope.

There were no sounds from above, however. No Maggie shrieked. The quiet of the house was unbroken. Finally she took the poker and tapped on the furnace itself, with unexpected results. Susie’s voice came from the top of the basement stairs.

“For God’s sake, stop that racket Amos,” she called. “Don’t tell me you’re building a fire in weather like this.”

Hilda stood still, and after a moment Susie banged the door and went away. When at last Hilda went upstairs to Mrs. Fairbanks’s room it was to find Maggie smiling dourly in the hall.