The Bobbsey twins' vacation in Colonial Williamsburg takes an exciting turn when they catch a thief, discover a howling monster, and find an old American flag hidden during the Revolution.
The Bobbseys take their dog, Chief, to the lumberyard to buy materials to build a dog house. While at the yard Chief digs a hole and burys a bone. When the Bobbseys go to give the bone back, it turns up missing again.
While staying with their cousins on Grand Cayman Island, the Bobbsey twins and their friends search for an exquisite art object and the thief who stole it.