Kirby's Last Circus — Ross H. Spencer

Birch Kirby is a middle-aged private eye with a penchant for drinking too much, singing Irish barroom songs, and befriending $25-a-night ladies-of-the-night. He is not exactly the smoothest private eye in Chicago.
But the CIA has noticed Kirby. They like his style. Nobody can be as genuinely inept as Kirby pretends to be, and they need someone with his imagination. After all, strange things are going on in the town of Grizzly Gulch, Illinois. The KGB keeps transmitting secret messages that, when decoded, read, “SAMD+23.” The CIA has been scratching their heads over that one, but they expect Kirby to break the case.
Three months behind in his rent, Kirby answers the call of duty and goes into deep cover as the bullpen catcher for the Grizzly Gulch No Sox, only to end up fighting off the No Sox's nymphomaniacal owner, Matilda Richwell, instead of the KGB. But through bumbles and accidents that would make Chevy Chase blush, Birch Kirby learns the meaning of SAMD+23.