A series of crime tales follows a former laboratory assistant who applies experimental psychological and physiological techniques to unravel puzzling cases. He adapts instruments such as the cardiograph, pneumograph and galvanometer and uses association tests and automatograph observations to expose involuntary reactions that reveal lies, motives or hidden memories. Each case presents a different mystery—missing persons, suspicious deaths and enigmatic evidence—resolved through careful measurement, observation and reasoning, emphasizing the application of scientific method to human behavior and the legal implications of objective tests in establishing credibility and guilt.