Yang is certain that someone is spying on him and Yin for the Night Master. In an effort to find out who, he and Yin use the Chronologicum to travel through time and see if any of their past adventures can reveal who the spy is. However, travelling through time seems to cause more trouble than good, as watching all the times that each of them had been hurt or laughed at by the other just serves to tear them apart! Can Yin and Yang set aside their differences to find out who the spy is, or will their petty fights end up erasing them from time forever?