They walked down the stone stairs

"Thanks," said van Heerden, pocketing the ticket, "it is of no use to me now, for I cannot wait. I gather that you have not disclosed the fact that this ticket is in your possession."
"Lower your voice!" he hissed menacingly. "I gather as much because Beale knew the ticket would not be in my possession now. If he only knew, if he only had a hint of its existence, I fear my scheme would fail. As it is, it will succeed. And now," he said with a smile, "time is short and your preparations must be of the briefest. I will save you the trouble of asking questions by telling you that I am going to take you along with me. I certainly cannot afford to leave you. Get your coat."
With a shrug she walked past him to the bedroom and he followed.
There was no tremor in her voice and she felt remarkably self-possessed.
"I am not asking out of idle curiosity, but I want to know whether I ought to take a bag."
She carried the little attache case back to the sitting-room.
"You have no objection to my taking a little light reading-matter?" she asked contemptuously. "I am afraid you are not a very entertaining companion, Dr. van Heerden."
"Excellent girl," said van Heerden cheerfully. "Take anything you like."
She slipped a book from the shelf and nearly betrayed herself by an involuntary exclamation as she felt its weight.
"You are not very original in your methods," she said, "this is the second time you have spirited me off."
"The gaols of England, as your new-found friend Milsom will tell you, are filled with criminals who departed from the beaten tracks," said van Heerden. "Walk out into the corridor and turn to the right. I will be close behind you. A little way along you will discover a narrow passage which leads to the service staircase. Go down that. I am sure you believe me when I say that I will kill you if you attempt to make any signal or scream or appeal for help."
She did not answer. It was because of this knowledge and this fear, which was part of her youthful equipment--for violent death is a very terrible prospect to the young and the healthy--that she obeyed him at all.
They walked down the stone stairs, through an untidy, low-roofed lobby, redolent of cooking food, into the street, without challenge and without attracting undue notice.
Van Heerden's car was waiting at the end of the street, and she thought she recognized the chauffeur as Bridgers.
"Once more we ride together," said van Heerden gaily, "and what will be the end of this adventure for you depends entirely upon your loyalty--what are you opening your bag for?" he asked, peering in the dark.
"I am looking for a handkerchief," said Oliva. "I am afraid I am going to cry!"
He settled himself back in the corner of the car with a sigh of resignation, accepting her explanation--sarcasm was wholly wasted on van Heerden.
"Well, gentlemen," said Milsom, "I don't think there's anything more I can tell you. What are you going to do with me?"
"I'll take the responsibility of not executing the warrant," said McNorton. "You will accompany one of my men to his home to-night and you will be under police supervision."
"That's no new experience," said Milsom, "there's only one piece of advice I want to give you."
"Don't underrate van Heerden. You have no conception of his nerve. There isn't a man of us here," he said, "whose insurance rate wouldn't go up to ninety per cent. if van Heerden decided to get him. I don't profess that I can help you to explain his strange conduct to-day. I can only outline the psychology of it, but how and where he has hidden his code and what circumstances prevent its recovery, is known only to van Heerden."
He nodded to the little group, and accompanied by McNorton left the room.