The character of Nick Carter has been around, in one form or other, since 1886. He’s been a P.I. and a spy. Some five authors wrote most of the early stories. I have no idea how many were involved in The Killmaster spy series. Other than Bill Crider of course.
In this one, master detective Nick Carter is investigating a minor robbery for a close friend. Staking out a French restaurant, he spots a waiter rushing out to leave in a cab. Curious, he enters and engages a head waiter, learning the floor the rushing waiter had worked. Two private dining rooms, one holding a dead woman shot through the head.
The head waiter later points out one man from one of the rooms, one John Jones. Jones is a cool customer, pointing out that if he had murdered the woman, tentatively identified as his wife, the woman he’d arrived with, though he claims different.
It’s left up to Nock Carter, along with his two assistants, to unravel the mystery.