Volume IX contains the nineteenth, twentieth, and twenty-first full-length Thorndyke adventures, published in 1938, 1940, and 1942, respectively. With each subsequent narrative, Thorndyke's skills and abilities grown and amaze.

The Stoneware Monkey - A young doctor's encounter with a modern sculptor opens the door to the curious world of art that is terrible, and those who seriously promote it anyway as something of value. When the sculptor dies, Thorndyke spots the importance of his curious stoneware monkey - a talentless object containing the clue to the solution.

Mr. Polton Explains - After assisting Dr. Thorndyke in his many adventures, it's time for Nathaniel Polton to tell his own story: His humble upbringing, the apprenticeships where he learned his many skills, his nearly total downfall, and how he was rescued by Thorndyke. Then, an incident from his youth provides the solution to a modern mystery.

The Jacob Street Mystery - An artist is pestered by his new neighbor, an abrasive woman who wants his opinion about her paintings. Then one day she vanishes, leading to the revelation of a most unique killer!