The journey of John and his family to visit an American grandmother takes them from London to Cape Cod and back again. A definite and quite successful attempt at bettering youthful Anglo American international relations provides a strong theme. First day out on the Queen Elizabeth, John runs into Roger, an American boy, and in the ensuing friendship between the two and John's sister, there develops the mystery of the missing sister of another friend of John's. This missing sister is found -- a victim of amnesia and given the time to choose between her new American and her true English family. But meanwhile the adventures, often described with the crackling of the activity that is peculiar to eleven-year-olds, at Granny Gay's cottage on the Cape and of a first view of the United States, are colorful cloth for the thread of the tale.