The girls wasted no time in words, and led him swiftly up the stairs, pausing before Mrs. Sanderson’s door.

“What shall we do if she’s gone?” whispered Betty, a sudden panic seizing her.  Then, without further delay, rapped smartly on the door.

At the answering “come in” they tumbled into the room, followed by Sergeant Mullins.  Then it was the second miracle happened!

Mrs. Sanderson started, stared, then rose tremblingly to her feet.

“My Willie boy!” she cried, groping toward him, dazed, unbelieving, incredulous.  “It’s my boy, my little son—­my—­baby—­”

Then Sergeant Mullins, with a hoarse cry, rushed across the room and gathered the little figure in his arms—­strong, man’s arms that crushed and hurt.

“Mother!” he cried.  “Oh, my mother!”

CHAPTER XXIV

MYSTERY EXPLAINED

The girls stared for a moment, dazed, bewildered.  Stared at the dark head bent in such passionate tenderness over the gray one, stared at the old hands patting the broad young shoulders, tremblingly, joyfully, incredulously, then, with a stifled gasp, turned and fled.

Betty closed the door softly and followed the girls into their own room where they sank down on arms of chairs or tables or the edge of the bed—­any place—­and went on staring, only this time at each other.

“Betty Nelson,” Mollie broke out at last, her eyes dark and wide, her voice awed, “did you ever in your life hear of such a thing?”

“Of course I never did,” answered Betty, her lips trembling, her eyes shining and wet.  “Not since my fairy-story days, anyway,” she added softly.

“But how,” Grace demanded, still too dazed to think clearly, “can Mrs. Sanderson’s son be William Mullins?”

“Goodness! how do we know?” returned Mollie, wiping two tears from the end of her nose.  “It’s all the biggest kind of a m-mystery, anyway.  Oh, dear, has anybody got a handkerchief?” as two other tears threatened to make their appearance.  “I didn’t know I had it in me to be such a goose.”

“We seldom do realize our possibilities,” drawled Grace, but Mollie was too busy wiping away the traces of her weakness to notice the insult.

“And to think,” Amy murmured softly, “that if that old motorcyclist hadn’t knocked Mrs. Sanderson down, she would have gone away without finding her son, and the chances are she would never have seen him again.”

“I suppose you think we ought to send the motorcyclist a vote of thanks,” remarked Mollie dryly, recovering herself a little.  “If he keeps on knocking old ladies down in the middle of the road and then gets himself arrested, he may be counted on to do a lot of good in the world.”

“I don’t see how you can say such silly things,” Amy began hotly, when Betty broke in pleadingly: