The Silent Speaker by Rex Stout

When a powerful government official scheduled to speak to a group of millionaire business men turns up dead, it is an event worthy of the notice of the great Nero Wolfe. Balancing on the edge of financial ruin, the orchid-loving private detective grudgingly accepts the case. Soon a second victim is found bludgeoned to death, a missing stenographer's tape causes an uproar, and the dead official speaks, after a fashion. While the business world clamors for a solution, Wolfe patiently lays a trap that will net him a killer worth his weight in gold.