The Wild Marauder — Ann Barker

Everyone in the neighborhood knows that Dora and Charlie are the perfect couple. But when it seems that Charlie's head has been turned by the London scene, Dora's younger sister Fenella decides to remind him of what he is missing. Her solution is to ask a stranger to flirt with Dora under Charlie's nose. The plan succeeds, but soon Fenella wonders whether her move was a wise one.