Volume IV contains the fourth, fifth, and sixth Thorndyke novels, published in 1914, 1922, and 1923, respectively. Covering different periods in the doctor's career, each of these shows Thorndyke's skills at their finest.

• A Silent Witness - When a young doctor finds a body that almost immediately vanishes, he's drawn into a dangerous plot which endangers his own life, and eventually leads the murderer to strike at Thorndyke's own door.
• Helen Vardon's Confession - In this unusual adventure, Helen Vardon tells her own story, in which her future is nearly stolen from her, and she is set on a path leading to her ultimate destruction - unless Dr. Thorndyke can save her.
• The Cat's Eye - An inheritance with ties to the Jacobite Rising of 1745 sets in motion a series of events that threatens not only Thorndyke's friends, but his own life as well.