For the first time this story takes our heroine away from her home ground in Buckinghamshire and on a trip to stay with a family in coastal Suffolk. No sooner has she got on to the small branch-line leading to the East Anglian resort than she finds herself embroiled in a mystery about a stolen painting. She quickly makes friends with Elizabeth and David Bale and fits comfortably into the life of the family. For the first time the reader sees signs that Penny is beginning to think about her appearance. The delights of a new dress and the opportunity for wearing it at a special dance are ideas that would never have crossed the mind of the younger Penny. The villain of the piece is easy to spot from the beginning but the dramatic intervention of a flood causes an exciting episode that makes Penny realise that every one has a mixture of qualities that go into their character. There are signs that Penny is growing up, though the author maintains a lot of the comic element by the dialogue between Penny and young David who spends most of his time coming up with impossible inventions.