The Case of the Stepdaughter's Secret — Erle Stanley Gardner

"There are just four ways to deal with a blackmailer," Perry Mason told Harlow Bancroft.

"First you pay the blackmailer off, thinking to get him off your neck. A blackmailer never quits!"

"Second, you go to the police." Bancroft shook his head decisively.

"Third." Mason continued, "you get the blackmailer on the defensive so he can't tell you what to do and when to do it."

"What's the fourth way?" Bancroft asked.

"I hardly recommend it," Mason said, "though sometimes it's been done with very satisfactory results. The fourth way is to kill the blackmailer."