“Chief!”

A stifled cry was heard in front of them; and a woman, a nurse, who was passing through the room, at once started running, lifted a curtain, and disappeared.

Don Luis rose, hesitating, not knowing what to do.  Then, after four or five seconds of indecision, he suddenly rushed to the curtain and down a corridor, came up against a large, leather-padded door which had just closed, and wasted more time in stupidly fumbling at it with shaking hands.

When he had opened it, he found himself at the foot of a back staircase.  Should he go up it?  On the right, the same staircase ran down to the basement.  He went down it, entered a kitchen and, seizing hold of the cook, said to her, in an angry voice: 

“Has a nurse just gone out this way?”

“Do you mean Nurse Gertrude, the new one?”

“Yes, yes, quick! she’s wanted upstairs.”

“Who wants her?”

“Oh, hang it all, can’t you tell me which way she went?”

“Through that door over there.”

Don Luis darted away, crossed a little hall, and rushed out on to the Avenue des Ternes.

“Well, here’s a pretty race!” cried Mazeroux, joining him.

Don Luis stood scanning the avenue.  A motor bus was starting on the little square hard by, the Place Saint-Ferdinand.

“She’s inside it,” he declared.  “This time, I shan’t let her go.”

He hailed a taxi.

“Follow that motor bus, driver, at fifty yards’ distance.”

“Is it Florence Levasseur?” asked Mazeroux.

“Yes.”

“A nice thing!” growled the sergeant.  And, yielding to a sudden outburst:  “But, look here, Chief, don’t you see?  Surely you’re not as blind as all that!”

Don Luis made no reply.

“But, Chief, Florence Levasseur’s presence in the nursing-home proves as clearly as A B C that it was she who told the manservant to bring me that threatening letter for you!  There’s not a doubt about it:  Florence Levasseur is managing the whole business.

“You know it as well as I do.  Confess!  It’s possible that, during the last ten days, you’ve brought yourself, for love of that woman, to look upon her as innocent in spite of the overwhelming proofs against her.  But to-day the truth hits you in the eye.  I feel it, I’m sure of it.  Isn’t it so, Chief?  I’m right, am I not?  You see it for yourself?”

This time Don Luis did not protest.  With a drawn face and set eyes he watched the motor bus, which at that moment was standing still at the corner of the Boulevard Haussmann.

“Stop!” he shouted to the driver.

The girl alighted.  It was easy to recognize Florence Levasseur under her nurse’s uniform.  She cast round her eyes as if to make sure that she was not being followed, and then took a cab and drove down the boulevard and the Rue de la Pepiniere, to the Gare Saint-Lazare.

Don Luis saw her from a distance climbing the steps that run up from the Cour de Rome; and, on following her, caught sight of her again at the ticket office at the end of the waiting hall.