She still struggled with the key, unconscious of his presence.

His tread on the thick carpet had been light; he had intended to catch her, beyond equivocation, in the act.
But now something about the lines of her stooping figure caused Henry Keenan to remove his hat, respectfully, before speaking to her.
"Could I assist you, madam ?" he asked, close to her side by this time.
She turned, with a start, though her loss of self-possession lasted but a moment.

But as she turned her startled eyes to him Keenan's last doubt as to whether or not it was a mere mistake withered away from his mind.

He knew, from the hot flush that mounted to her cheeks and from the mellow contralto of her carefully modulated English voice, that she belonged to that vaguely denominated yet rigidly delimited type that would always be called a woman of breeding.
"If you please," she said shortly, stepping back from the door.
He bent over the key which she had left still in the lock.
As he did so he glanced at the number which the key, protruding from the lock, bore stamped on its flat brass bow.

The number was Thirty-seven, while the number which stood before his eyes on the door was Forty-one.
Under ordinary circumstances the apparent accident would never have given him a second thought.