This book contains twelve of Professor Kennedy's adventures. The interesting thing about these stories is Kennedy uses newly discovered science from his time period, which we take for granted today. The title story features the use of special inks. One which disappears in sunlight and one which appears in sunlight, so that the text on a note found in possession of a murder victim changes completely, making it almost impossible for Kennedy to track down the killer. Each story features a fascinating look at life in the early 20th century, and even includes some action along the way.