“Goodness, don’t you even see there is a mystery?” she cried, facing them impatiently.  “How in the world could Sergeant Mullins ever be Mrs. Sanderson’s son?”

“You’d better ask ’em,” chuckled Mollie.  “They both seemed so tolerably sure of it that we’ve taken it for granted.  What’s the deep, dark mystery?”

“Grace means,” it was Amy who acted the peacemaker this time, “that it’s strange about the name.”

“And, of course, it is,” Betty added gravely.  “Sergeant Mullins should by all rights be Sergeant Sanderson.”

“And Mrs. Sanderson couldn’t have known about his being called Mullins,” Grace broke in eagerly, “because we’ve spoken to her of Sergeant Mullins more than once, and she never acted as though more than casually interested.”

“Well, but I suppose that’s easily enough explained,” said Mollie, who was in no mood for details—­the actual occurrences being wonderful enough in themselves to occupy her attention for some time to come.  “People often enough change their last names for some reason or other.”

“Then you mean,” said Grace, “that William Mullins is really William Sanderson?”

“A fair assumption,” returned Mollie dryly.  “Unless Mrs. Sanderson’s name is Mullins.”

“Perhaps the best way,” suggested Betty peaceably, “would be to wait and let Mrs. Sanderson tell us about it.”

“Wait—­” Grace was beginning, when a gentle tap sounded on the door and Betty flew to open it.

On the threshold stood Mrs. Sanderson, her eyes red with weeping, yet her whole face so transformed with joy that the girls would hardly have recognized her as the Mrs. Sanderson of that morning.  Instinctively they glanced over her shoulder, expecting to see the tall figure of Sergeant Mullins looming in the background, but he was nowhere to be seen.

“He’s—­he’s gone,” said the little old lady tremulously, seeming to interpret their glances, at the same time coming timidly into the room.  “He told me to tell you,” her face lighted up still more with that wonderful inward joy, “that he would have stayed and thanked you young ladies, but he’d made sort of an idiot of himself—­so he said—­an’ would be around later, instead.”

“And is he really—­really—­really your son?” cried Betty, unable to contain herself longer, pressing the old lady into a chair and kneeling down before her eagerly.  “Oh, we knew you’d come and tell us!  We’ve been so very happy for you.”

“Yes, he’s my Willie boy,” answered the little old lady, speaking dreamily as though even yet she was not able to grasp the wonderful thing that had happened to her.  “It’s strange when I come to think of it how I knew him right away because, you see, I’ve always sort o’ thought of him as my little son, my baby, and in my mind I’ve always seen him as he was that day he ran away.  But he’s really just the same—­my little Willie boy—­only taller and sort o’ broader in the shoulders an’ handsomer—­” her voice broke and Betty slipped a sympathetic little hand in hers while the girls gathered closer.