by Joan Lowery Nixon (1989)
Sixteen-year-old Mary Elizabeth's summer job at an expensive health club turns out to be more exciting than she bargained for when a series of mysterious events culminate in murder.
Astrid Lindgren. [Dt. von Karl Kurt Peters
While three children are waging an imaginary war against their three friends, they find themselves involved in an actual murder case, which they solve with clues revealed by subsequent events of their own war.
Joan Lexau
When his neighbor finds dog food in strange places all over his house, Willy Nilly asks Miss Happ, a witch, to help solve the mystery.
Carolyn Keene
The Dean of Emerson College enlists Nancy to investigate the thefts of a valuable substance being used in a top-secret experiment. But when Nancy discovers that the experiment involves biological mutations, she knows she must find the culprit before the lives of everyone on campus are endangered.
John Peterson
Weasel is after something, and he's going to trick Flying Squirrel to get it. But Flying Squirrel has a friend, Mr. Bat, who isn't going to sit around and let Weasel get away with it!