It’s often the case that a line can be drawn in an author’s body of work, past which they notably change, usually for the better: John Dickson Carr after Poison in Jest (1932), say. It is, however, rare that such a line passes through one of their works, as it does for Anthony Berkeley in Roger Sheringham and the Vane Mystery (1927). Prior to this Berkeley had written The Layton Court Mystery (1925) and The Wychford Poisoning Case (1926), which innovated in this newfangled GADisphere but seemed interesting if minor, and are not readily discussed a century later. And after it came the likes of The Poisoned Chocolates Case (1929) and Not to be Taken (1938), reprints of which were greeted with no small delight in recent years.
The Invisible Event 