Aztec Sword - A Calvin Carter, Railroad Detective, Adventure, #3

Actor turned detective Calvin Carter stands on his favorite place--a stage--when armed bandits attack. Carter and his partner, Thomas Jackson, foil the robbery, and the surviving gunman snitches the name of the mystery man who hired the gang. Both men soon die, taking their secrets to the grave. Turns out, the entire robbery was an elaborate distraction. In the melee, a master thief with a unique calling card swipes a prized artifact: a macuahuitl, an Aztec sword, dating back to the Spanish conquest of the New World.
But when Carter and Jackson are assigned to track down and recover the sword, those men who know about the macuahuitl start dying, one by one. If Carter and Jackson aren't careful, they will be next.