"All right," agreed Bart, "only I wish I knew who that man was." The time was to come when the boys would have given a great deal to have been able to penetrate the identity of the mysterious stranger. But the three chums gave little heed to that now, for they were intent on playing a joke that Bart had evolved. A little later, finding the front door unlocked, they were inside the school, just as the distant town clock boomed out the hour of midnight.