From The Perry Mason TV Show Book
Here it is: the case that Perry Mason lost . . .

The jury returns from their chambers to give the verdict on case number CR11532; the State of California vs. Perry's client, Janice Barton. They find Janice guilty of murdering her invalid Aunt Amanda and sentence her to die in the gas chamber.

How did Perry manage to lose a case? Well, for one thing, Janice lied about where she was at the time someone gave her aunt poison instead of medicine.

Perry is troubled. The evidence stacks up against Janice but he still has a hunch. And as long as he has one of those hunches, he'll keep looking for the real killer. In this case, it turns out to be someone very unexpected.