Arnold was suddenly conscious that Sabatini, for the first time since he had known him, was in earnest.  The lines of his marble-white face seemed to have grown tenser and firmer, his manner was the manner of a man who meets a crisis.

“Turn your head and look inland,” he said.  “You follow the lane there?”

Arnold nodded.

“Quite well,” he admitted.

“At the corner,” Sabatini continued, “just out of sight behind that tall hedge, is my motor car.  I want you to land and make your way there.  My chauffeur has his instructions.  He will take you to a village some eight miles up the river, a village called Heslop Wood.  There is a boat-builder’s yard at the end of the main street.  You will hire a boat and row up the river.  About three hundred yards up, on the left hand side, is an old, dismantled-looking house-boat.  I want you to board it and search it thoroughly.”

Sabatini paused, and Arnold looked at him, perplexed.

“Search it!” he exclaimed.  “But for whom?  For what?”

“It is my belief,” Sabatini went on, “that Starling is hiding there.  If he is, I want you to bring him to me by any means which occur to you.  I had sooner he were dead, but that is too much to ask of you.  I want him brought in the motor car to that point in the lane there.  Then, if you succeed, you will bring him down here and your mission is ended.  Will you undertake it?”

Arnold never hesitated for a moment.  He was only too thankful to be able to reply in the affirmative.  He put on his coat and propelled the punt a little further into the rushes.

“I’ll do my best,” he asserted.

Sabatini said never a word, but his silence seemed somehow eloquent.  Arnold sprang onto the bank and turned once around.

“If he is there, I’ll bring him,” he promised.

Sabatini waved his hand and Arnold sped across the meadow.  He found the motor car waiting behind the hedge, and he had scarcely stepped in before they were off.  They swung at a great speed along the narrow lanes, through two villages, and finally came to a standstill at the end of a long, narrow street.  Arnold alighted and found the boat-builder’s yard, with rows of boats for hire, a short distance along the front.  He chose one and paddled off, glancing at his watch as he did so.  It was barely a quarter of an hour since he had left Sabatini.

The river at this spot was broad, but it narrowed suddenly on rounding a bend about a hundred yards away.  The house-boat was in sight now, moored close to a tiny island.  Arnold pulled up alongside and paused to reconnoiter.  To all appearance, it was a derelict.  There were no awnings, no carpets, no baskets of flowers.  The outside was grievously in need of paint.  It had an entirely uninhabited and desolate appearance.  Arnold beached his boat upon the little island and swung himself up onto the deck.  There was still no sign of any human occupancy.  He descended into the saloon.