Case of the Poison Pen-Pal

Most of the action takes place in San Francisco. Perry Mason gets involved by way of Paul Drake.

At the heart of the plot is the correspondence of two young girls. They write about what they know and what they hear. And one of them has heard her father, Peter Gregson, discuss a pending merger involving the firm where he is president. The other girl has become a conduit of inside information for an unethical man who is dating her mother.

The chief officers of Gregson Cannery are in deep discussion about the fate of the firm. For some reason the price of shares has risen 33 percent in recent days. The board needs to acquire 65,000 additional shares for the success of the merger but the intent was to buy them at the old price.
Lee (cousin slackard): As it stands right now, we’re bankrupt if the merger doesn’t go through and we’re bankrupt if it does.
Aunt Wilma: If you paid more attention to your job and less to your outside interests, this wouldn't come as such a shock to you, either.
Peter: Gregson Cannery stock hasn’t fluctuated one point up or down in the last 30 years.

Gregson Cannery is a family firm headed by the odious Wilma Gregson. She is assaulted in her home one night. The company officers are standing watch at the hospital when the doctor comes in to say Aunt Wilma has died. The family isn't too upset. One rattles off a quote from Kipling.

Lee: "Oh, the years we waste and the tears we waste. And the work of her head and hand belong to a woman who did not know. " Isn’t anybody going to cry for dear Aunt Wilma?
Peter: Oh, shut up, Lee. The hand that fed you is dead. Don’t bite it now.

The defendant is the former private secretary of Peter Gregson. The prosecutor is some San Francisco hotshot. Sounds like he went to school with Hamilton Burger, though.
DA: Aside from trying to fish in irrelevant waters, counsel is badgering this witness.

PM to witness: Are you telling the truth or deliberately lying in order to give (spoiler) an alibi?

Someone has an inferiority complex.
Witness: And not only that, but by making all that money I could prove that I was the smart one. Me!