"Mystery Stories Based on Real Cases Solved By Government Agents". Good stories, a small amount of "negro" dialog that I found...embarrassing. Except for that tiny bit I enjoyed reading this old-timey book a lot. I read the Project Gutenberg e-book version.
Quote:
"A slip of oiled paper," he muttered. "By the Lord Harry! here it is!" and he produced a pencil which his trained fingers told him was lighter than it should be.-- A hollow pencil!!