Mystery of the Skinny Sophomore — Jerry B. Jenkins

The older sister of one of the members of the Baker Street gang has changed. She seems like a different person and it has affected her brother. He's upset and worried. He wants to know what has gotten into her. Not only is she not acting at all like herself, but she also seems to be wasting away. Always slim, now she's skin and bone. Can the Baker Street boys find out what's wrong? See how Dallas and his friends solve the mystery and try to live their lives of faith in a modern world.