Carpentaria and Pauline continued to stand motionless outside the house, both of them hesitant, recoiling before the circumstances which faced them. The night remained clear, almost brilliant.

“The entire situation is changed,” said Carpentaria at length. “A new factor has entered into it.”

“What factor?” Pauline demanded.

“Why, your sister, of course!” he replied, with a slight smile that disclosed momentarily the quizzical male person in him. “Consider how it complicates the affair. If I had to deal only with the mysterious individual with grey hair and a blue suit—perhaps you do not know that he calls himself Jetsam?—I could go to work in a simple masculine fashion, and in the end one of us would suffer, probably he. But with a woman in the case——”

“How can you be sure,” Pauline interrupted him, “that Rosie is in the case?”

“Can you doubt it?”

“I cannot understand why she should behave so!”

“Perhaps she knew him before,” Carpentaria hazarded.

“Never,” said Pauline positively—“never.”

“Then he has certainly been able to exercise a most remarkable influence over her.”

“Not a hypnotic influence, or anything of that kind?”

“Perhaps an influence of quite another kind—quite another kind.”

“But Rosie is scarcely half his age.”

“Do these things depend on age?” cried Carpentaria. “They depend on glances, sympathies, and trifles even more subtle than sympathies. Besides, she is more than half his age.”

“Oh,” murmured Pauline, with a sudden wistful appeal in her voice, “I shall trust you to help me, Mr. Carpentaria. Rosie may be in danger; she may be doing something very foolish, mixing herself up like this in the kidnapping of poor Cousin Ilam. What is to be done?”

“She is decidedly doing something very foolish,” said Carpentaria, “foolish, that is, from a mere ordinary common-sense point of view. But I don’t think she is in any danger. I don’t think that either she or you are the sort of woman that gets into danger without very good cause. As to what is to be done, I have an idea. Mrs. Ilam will be all right alone?”

“Yes; for a few hours, at any rate.”

“Then will you come with me to the river? I have some investigations to make.”

“Certainly,” said Pauline.

And as they crossed the Oriental Gardens for the second time that night, he told her what he knew about the use, or rather the abuse, of the automobile.

The marble parapet of the immense terrace of the gardens stood a dozen feet above the level of high tide. The terrace was continuous from end to end, but in several places it formed a viaduct over paths that ran from the gardens at a steep slope down to the bed of the river. It was one of these paths, a specially clayey one, at the point where it ran under the terrace, that Carpentaria suspected the automobile of having taken. Assuming his suspicion to be correct, the automobile could only have descended to the Thames, and then, if the tide gave room, turned round and returned; or, if the tide did not give room, backed out without turning.

“Its sole purpose,” said Carpentaria, as they talked the matter over, “could have been to pass something to a boat. Don’t you think so?”

“Yes,” Pauline agreed, and then she added, “unless they merely wanted to throw something into the river.”

“What!” He cried; “a corpse?”

“No,” she said calmly. “I was thinking of the two thousand five hundred pounds in gold that you told me had been stolen.”

He paused.

“This is really very clever of you,” he said. “But why should they throw it into the river.”

“Well,” she said, “it’s high tide, or rather it was, about an hour and a half ago. They might have sunk the money, intending to recover it at their leisure during the night when the tide sank.”

“Yes, I must repeat,” he said; “this is really very clever of you.”

They were already beginning to descend the broadest of the three paths which led from the level of the gardens to the level of the river, and the wheelmarks of an automobile were clearly visible thereon, when Carpentaria halted.

“Suppose,” he whispered, “they are there now?”

“Who? Mr. Jetsam and my sister?”

“No, not your sister. Mr. Jetsam and his—other accomplices—whoever they may be. I do not imagine that your sister has been concerned in the actual—er—affair. Indeed, she was at home with you at the time. But if Jetsam, for instance, should be down there now, alone or with others, there might be a row on my appearance. I will therefore ask you to stay where you are, Miss Dartmouth.”

She shook her head.

“I have begun,” she said, “and I will go through with it. Besides, what danger could there be? People don’t go shooting and killing promiscuously like that.”

“Oh, don’t they!” Carpentaria exclaimed.

“Moreover, I have no fancy to be left alone here now,” she added. “And most likely there isn’t anyone there at all.”

“Hush!” said Carpentaria. “Can’t you hear the splash of an oar? Listen!”

They listened.

“Yes,” she murmured. “And is not that the noise of a boat crunching on the beach?”

The path disappeared mysteriously before them under the terrace; they could not see the end of it. But the sound-waves came clearly enough through the little tunnel.

“We will go back,” said Carpentaria, “and slip on to the terrace. Behind the parapet we can see anything that may happen to be going on. But quietly, quietly, dear lady.”

In a few moments they were creeping across the broad terrace. Simultaneously they bent down, side by side, under the parapet and looked between its squat, rounded pillars at the water below.

Pauline gave a slight smothered cry, which Carpentaria, with an imperious gesture, bade her check.

“Not a word,” he whispered in her ear.

Rosie—Rosie and no other—was manoeuvring a boat off the shore. Her face, her dress, her hat, were plainly visible in the moonlight. She stood up in the boat, and by means of a boat-hook hooked to a large oblong stone, drew the boat to the shore. She then seized the painter and jumped lightly out.

The curious thing was that she went directly to the large oblong stone, and with a great effort, lifted it up in her arms, tottered with it to the boat, and deposited it therein. Carpentaria perceived then that the stone was not a stone, but one of the coffers in which was kept the gold of the City of Pleasure. He perceived also that, attached to the coffer, was a dozen feet or so of rope with a cork float at the end. Rosie followed the coffer into the boat, pushed off, and then, at a distance of a few yards from the shore, pitched the coffer into the river. This done, she landed, made fast the painter of the boat to an iron ring in the wall of the embankment and departed; and she did it all rather neatly.

Immediately she had disappeared under the terrace, Pauline cried, starting up:

“I must go to her—I must ask her what she means by doing such things.”

“Pardon me,” said Carpentaria; “you must do nothing of the kind. I most seriously beg you to do nothing of the kind. By interfering now you may spoil the coup which we may ultimately make.”

“I don’t quite comprehend you,” Pauline observed. “Miss Dartmouth,” he addressed her excitedly, “there can be no doubt in your mind now that your sister is concerned in this plot, whatever it is. I am perfectly convinced that her motives are good, honourable, kind-hearted. But she is concerned in it. We must, therefore, so far as we can, treat her as one of the conspirators——”

“But surely——”

“Always with profound respect,” said Carpentaria. “Had the person in the boat been any other than your sister, should we have revealed ourselves? Certainly not! We should have followed the plot to its next development, with this advantage—that we knew something which the conspirators imagined to be a secret. The fact that the person in the boat was your sister must not alter our course of conduct. And permit me to add, Miss Dartmouth, that you first approached me on behalf of my sister. We owe something to her, do we not?”

“Yes,” said Pauline in a low voice. “Then what do you mean to do next?”

“I suggest that we go back to your house, to see whether your sister has returned. May I ask whether, when you last spoke to her, she gave you to understand that she meant to stay with Mrs. Ilam?”

Pauline breathed a reluctant affirmative.

“No hint that she was going out?”

“None. And——”

“And what?”

“Oh, dear!” Pauline sighed. “Must I tell you? Yes, I must! I’m sure Rosie is acting for the best, but really it was not her turn to watch Mrs. Ilam to-night.”

“Whose turn was it?”

“The nurse’s.”

“And your sister changed the rotation?”

“Yes. She said the nurse needed a holiday, and told her she could go away for twenty-four hours, and that she would take her place.”

“What time was that?”

“About six o’clock this evening, I think.”

“And where has the nurse gone?”

“The nurse has gone to a concert at Queen’s Hall, and will sleep at the house of some friends at Islington.”

“And does your sister imagine you to be in bed?”

“I expect so,” said Pauline.

They slowly returned to the neighbourhood of the bungalows. Carpentaria wanted to hurry, but it seemed as though Pauline was being held back by some occult force. As a matter of fact, she dreaded the moment when she should re-enter the house. But at length, they stood once again by the doorstep of Josephus Ilam.

“What am I to do?” Pauline demanded sadly. “What do you think will be the best thing to do?”

“We have not seen your sister in the gardens,” said Carpentaria. “She has most probably returned. She would not be likely to leave Mrs. Ilam for very long, would she? Go and see if she has returned, if she is in Mrs. Ham’s room. And if she is, question her.”

“But how? What am I to say? Am I to ask her if she has been out?”

“By no means!” said Carpentaria promptly. “You are to pretend that you know nothing. You must approach her diplomatically. Either she will tell the truth or she will——”

“Lie! Lie!” cried Pauline. “Say it openly! Say the word! Admit that you are persuading me to behave despicably to the creature who is dearest to me in all the world.”

“If there is duplicity,” Carpentaria answered, “you, at any rate, did not begin it. We are convinced of your sister’s good intentions. What else matters? In a few days, perhaps to-morrow, all will be explained. Let me entreat you to go at once. I will await your report.”

She shook her head sadly, opened the door with her latchkey, and was just about to shut it when Carpentaria stopped her.

“One moment,” he said. “You have told me your sister believes you to be in bed.”

“I say ‘probably.’”

“It is important that she should not be undeceived. I need not insist. You can easily make it appear that, having been awakened by some noise, you have got up. Eh?” And he smiled.

She tried to smile in return, and disappeared from his view. Within the house, she crept upstairs, and into her bedroom, feeling like a thief. When she emerged therefrom she had put on a peignoir, and her coiffure was disarranged. She went to the door of Mrs. Ham’s room, and listened intently. There was not a sound. If she was to obey Carpentaria she must enter, and she must wear a false mask: to that sister to whom she had all her life been as sincere as it is possible for one human being to be to another. Well, she could not enter—she could not enter! Her legs would not carry her through the doorway. And so, instead of going in, she called:

“Rosie!”

But her voice was so weak that she scarcely even heard it herself.

No reply came from the interior. And she called again, this time quite loudly:

“Rosie, dear!”

Then she opened the door an inch or two. There was a rush of skirts across the room, and Rosie appeared. She was evidently in a state of extreme excitement.

“What’s the matter? Are you ill?” asked Rosie.

“I—I was wakened by some noise or other,” said Pauline painfully, and it appeared to her that Carpentaria was whispering in her ear the words that she must say. “And—and—I—I thought perhaps something had gone wrong here.”

“No,” was Rosie’s reply. “But how queer you look, darling! You must have had a nightmare. You have quite startled me.”

Pauline did not answer at once.

“You aren’t undressed! You haven’t lain down,” she said at length. “I thought you could always sleep very well on that sofa.”

“So I can,” said Rosie. “But I’ve been reading. And besides—it’s rather upsetting about Cousin Ilam. I wonder where he can be.”

“Oh!” Pauline remarked summarily, “he’s pretty certain to turn up to-morrow. I expect he’s gone into town.”

Rosie yawned.

“Yes,” she agreed.

“Well, good-night, darling,” said Pauline, and took Rosie’s hand. .

“Good-night.”

“How cold your hand is!” Pauline observed, with an inward tremor. “Have you been out?”

“Been out? What do you mean?”

“Outside on to the balcony?”

“No. I haven’t stirred from my chair, darling. Bye-bye.”

They stared at each other for an instant, each full of dissimulation, and yet also of love, and then they kissed one another passionately, and Pauline departed. They were women.