Their next adventure took them to Ocean View and centered about a mysterious box they found in the sand.

Then followed that glorious trip to Pine Island.  An aunt of Mollie Billette had turned her bungalow over to the Outdoor Girls for the summer.  During their strenuous adventures the girls had made many friends among the boys and young men of Deepdale, and four of these had asked and been granted permission by the girls to accompany them to Pine Island and pitch their camp in the woods near by.

One of the young men was Allen Washburn, a rising young lawyer and a great admirer of Betty.  Another was Will Ford, Grace’s brother, and a third was his high school chum, Frank Haley.  The fourth, Roy Anderson, had been drawn into the circle chiefly through his admiration for Grace.

During that eventful summer on Pine Island the young people had accidentally discovered a gypsy cave, concealed by underbrush, and had succeeded not only in rounding up the band of gypsies but in recovering several valuable articles that had been stolen from the girls.

Their last adventure, related in the volume directly preceding this one, and entitled “Outdoor Girls in Army Service,” found the girls and boys again at Pine Island, but under very much altered conditions.  America had entered the great World War and all the boys but Will Ford had volunteered.  Later, the boys were called to Camp Liberty, some distance from Deepdale, and the girls conceived the plan of opening a Hostess House for the benefit of the relatives and friends of the boys.  The plan worked out very satisfactorily.

While still at Pine Island the girls and boys had come upon a suspicious looking man in the woods.  Upon finding himself discovered the man had made his escape, but in his hurry had dropped a letter which the girls found to their disgust was written in code.  They decided that the man must have been a German spy.

At Camp Liberty the girls succeeded in rounding up the spy, and found, to their surprise, that Will Ford, who was in the Secret Service, had been engaged all that time in tracking him to earth.  Will, having accomplished his mission, immediately enlisted.

Now, at the time this story opens, the girls were still at the Hostess House and looking forward apprehensively to the time, now imminent, when the boys would be ordered across the sea to fight for the country they loved.

“I’ll go with Grace,” volunteered Amy, in answer to Betty’s request for water.  “I don’t suppose we can find any, but we’ll try.”

The two girls hurried off, leaving Mollie and Betty to loosen the woman’s collar and rub her cold hands.

“Betty, Betty, is she dead?” Mollie was crying for perhaps the hundredth time, when the woman herself answered the question by opening her eyes and looking vacantly about her.

“Who—­are—­you?” she queried faintly, struggling to rise.

“Oh, please don’t try to get up just yet,” Betty pleaded, looking very sweet and charming in her solicitude.  “I don’t think you’re strong enough—­”