Fade to Black - Robert Goldsborough

A soda war explodes into murder for Nero Wolfe, "one of the two or three most beloved detectives in fiction" (Publishers Weekly).
For the men of Madison Avenue, the battle between soft-drink giants Cherr-o-key and AmeriCherry seems heaven sent. For years now, the firm of Mills/Lake/Ryman has fought to help Cherr-o-key become the nation's favorite fizzy cherry soda, but each time they come up with a new slogan, mascot, or jingle, AmeriCherry somehow beats them to it. There's a mole inside the agency, and only Nero Wolfe can ferret him out. Although he's as round as a cherry himself, Wolfe has no taste for soft drinks. But the question of industrial espionage is too sweet for him to resist, and so with assistant Archie Goodwin at his side, he sets out to end this vicious corporate feud. Only when the first adman dies does he realize that a marketing war can be just as dangerous as the real thing.