Murder at Breakfast — Steve Demaree

A homicide detective receives a call that a woman has been found dead in her apartment in an apartment building for well-to-do elderly people. It turns out she had been poisoned, but it remains to be seen as to where, when, and how the poison was administered. Her apartment was locked, the door latch was in use, and she was found seated at a table, with her face in a plateful of food. Yet none of the food on that plate contained poison, and she was dead before the food was sent up to her apartment.