The Clue in the Diary (Nancy Drew, Book 7)

Nancy and her friends Bess and George, on their way home from a carnival, discuss a financially struggling Swedish immigrant, Mrs. Swenson, and her daughter, whom the girls have just helped to enjoy the carnival attractions by being their hosts for the evening. As they are driving, a luxurious roadside estate bursts into flames. The girls park the car and make sure that no one is trapped inside. In doing so, Nancy sees someone fleeing the property, and discovers an anonymous Swedish diary on the ground. She picks up this clue, and as firefighters and gawkers arrive on the scene, she notices an attractive young man moving her car away from the flying embers. At first suspicious of Ned Nickerson, Nancy warms to him when he helps her out of a jam. Ned proves to be a good friend, and is a perennial admirer of Nancy's from then on. Meanwhile, Mrs. Swenson's husband is missing, and she identifies his diary as the one picked up at the fire. To top it all off, the owner of the burned house, Felix Raybolt, is missing, and his wife claims Joe Swenson has murdered her husband. Raybolt, it turns out, swindles inventors like Swenson out of their patents and copyrights, and used one such invention to start the fire.