From the ranch Dave and his chums returned again to Oak Hall, as recorded in "Dave Porter and His Rivals." Then came the Christmas Holidays, and Dave went back to Crumville, where he and his folks were now living with the Wadsworth family in their elegant mansion on the outskirts of the town. Directly after Christmas there was a thrilling jewelry robbery at Mr. Wadsworth's factory. It was Dave, aided by some of his chums, who got on the track of the robbers and trailed them to the South and then to sea, as related in "Dave Porter on Cave Island." When our hero and his chums went back to Oak Hall they imagined that their adventures were at an end. But soon came in news of a strange man who was terrorizing the neighborhood. Some very unusual things happened, including an attempt to blow up a neighboring hotel. Some of the students were thought guilty, and fearing arrest, they fled in terror, as told of in "Dave Porter and the Runaways." Dave was not one of those who ran away, but he did go after the others, and made them come back to face the music, and also helped to clear up what had been a great mystery. Then all the boys graduated from Oak Hall, Dave receiving high honors. It is needless to say that our hero at that time was one of the happiest boys in the world. His folks and Jessie Wadsworth came to the graduation, which was celebrated with big bonfires, music by a band, and refreshments in the gymnasium. Dave had promised Roger Morr that he would pay the Senator's son a visit. He did so, along with Phil and some others, and on that occasion heard about a gold mine which had been willed to Mrs. Morr, and which had been completely swallowed up by a landslide. Numerous searches had been made for this lost mine, but up to that time without result. "Let us go in search of the lost mine," Dave had said. And how he and Roger and some of the others made the trip to the West and went on a hunt for the mine has been told in detail in the volume entitled "Dave Porter in the Gold Fields." While the lads were on this quest, they again fell in with Link Merwell, who with Job Haskers, a former teacher at Oak Hall, was also trying to locate the lost mine. The two parties had many adventures, and when at last the missing mine was relocated, there came another landslide which nearly cost Dave and his friends their lives. When they finally reached a place of safety they were joined by a man from the other party who had suffered severely, and who told them that Link Merwell and Job Haskers, as well as a third person of the party, had been swept away to their death. Later on Dave and his friends had looked for the missing persons, but had been unable to locate them.