The fourth entry in A. A. Fair (Erle Stanley Gardner)'s Donald Lam-Bertha Cool series is set in 1940. It's still early in the game for Donald and Bertha, but the series is hitting its stride, and while there are still a couple of wrinkles to be worked out, the general parameters of the series are now in place. Bertha is the big, tough, cheap, no-nonsense half of the team, while Donald is the small, brainy guy who is irresistible to women and who always seems to be half a step ahead of everyone else in the game, most especially, Bertha, who constantly nags and questions whatever he's doing until he inevitably pulls a rabbit out of the hat and saves everyone's bacon.
The case opens when Bertha hires a Japanese judo instructor to teach Donald how to defend himself. He's a small guy and is constantly getting beaten up. He's also a valuable asset, and Bertha would like to see him survive. (It's 1940, and so there are a lot of politically incorrect references to the "Jap" instuctor.) This proves to be a difficult proposition, and the lessons aren't going very well, but then a potential client drops by in the middle of one of Donald's lessons. The guy needs a private detective to check up on his daughter and conceives of the notion of having Donald come out to his house on the pretense of giving him physical fitness tips as a means of getting Donald close to the daughter.
It's a hare-brained scheme, especially since Donald is failing miserably at his his own lessons, but for a hundred bucks a day, Bertha thinks it's a great idea. Once in the household, Donald quickly concludes that the beautiful, feisty daughter is being blackmailed. All sorts of other shenanigans are taking place, and pretty quickly, somebody gets killed and all hell breaks loose. Donald will have to think very quickly to survive this case and save everyone involved, including the client and his boss.
Like virtually every other book written by Gardner, the Perry Masons included, the whole thing gets pretty preposterous, but it's still a lot of fun. And if you just suspend disbelief and go along for the ride, it's a very entertaining way to spend a winter evening.