Summers at grandmother's Connecticut farm are always exciting to eleven-year-old Denny and his nine-year-old sister, Joan. But it seems that Peter, the housekeeper's boy, is going to make this summer a little less agreeable with his strange unfriendly ways. Then, there have been three robberies at grandmother's, each time the thief stealing nothing but toys, and Denny, in spite of his growing fondness for Peter, fears that he is the culprit. It takes a beautiful blue vase and a torn sheet from a diary to vindicate Peter and lead to the apprehension of Smiley Magwood, notorious jewel thief. What is the secret of the blue vase, and why should an international thief be so interested in children's toys? Not only are these questions answered, but as a result of the mystery Peter learns the value of friendship. This is a fast paced, meticulously worked out mystery, combining the warmth of a family story with the suspense of a who-dun-it.