“It’s Port Said!” Quest exclaimed.  “What the mischief—­have we turned round?  Say, Professor, has your compass got the jim-jams?”

“I don’t care where it is,” Lenora faltered, with tears in her eyes.  “I thought Port Said was a horrible place, but just now I believe it’s heaven.”

The Professor turned towards them and shook his head.

“Can’t you see?” he pointed out.  “It’s a mirage—­a desert mirage.  They are quite common at dusk.”

Lenora for a moment was hysterical, and even Laura gave a little sob.  Quest set his teeth and glanced at the Professor.

[Illustration:  “WHILE WE ARE WAITING, LET’S GO IN AND BE SHOCKED!”]

[Illustration:  “YOU MUST THANK HIM FOR YOUR LIVES—­THE MONGARS NEVER TAKE PRISONERS.”]

“Always water near where there’s a mirage, isn’t there, Professor?”

“That’s so,” the Professor agreed.  “We are coming to something, all right.”

They struggled on once more.  Night came and brought with it a half soothing, half torturing coolness.  That vain straining of the eyes upon the horizon, at any rate, was spared to them.  They slept in a fashion, but soon after dawn they were on their feet again.  They were silent now, for their tongues were swollen and talk had become painful.  Their walk had become a shamble, but there was one expression in their haggard faces common to all of them—­the brave, dogged desire to struggle on to the last.  Suddenly Quest, who had gone a little out of his way to mount a low ridge of sand-hills, waved his arm furiously.  He was holding his field-glasses to his eyes.  It was wonderful how that ray of hope transformed them.  They hurried to where he was.  He passed the glasses to the Professor.

“A caravan!” he exclaimed.  “I can see the camels, and horses!”

The Professor almost snatched the glasses.

“It is quite true,” he agreed.  “It is a caravan crossing at right angles to our direction.  Come!  They will see us before long.”

Lenora began to sob and Laura to laugh.  Both were struggling with a tendency towards hysterics.  The Professor and Quest marched grimly side by side.  With every step they took the caravan became more distinct.  Presently three or four horsemen detached themselves from the main body and came galloping towards them.  The eyes of the little party glistened as they saw that the foremost had a water-bottle slung around his neck.  He came dashing up, waving his arms.

“You lost, people?” he asked.  “Want water?”

They almost snatched the bottle from him.  It was like pouring life into their veins.  They all, at the Professor’s instigation, drank sparingly.  Quest, with a great sigh of relief, lit a cigar.

“Some adventure, this!” he declared.

The Professor, who had been talking to the men in their own language, turned back towards the two girls.

“It is a caravan,” he explained, “of peaceful merchants on their way to Jaffa.  They are halting for us, and we shall be able, without a doubt, to arrange for water and food and a camel or two horses.  The man here asks if the ladies will take the horses and ride?”