Mack Stoly was a Secret Service agent stationed in Denver and was in charge of the security of President Noah Grace's Victory Tour on December 15th, 1951. Stoly was receptive in having Sentinel Nathan Hale in enforcing extra security from the Sentinels given not only to protect any possible Chimera attack but due to the fact that the President's Chief of Staff William Dentweiler demanded for a much larger crowd for the celebration. In which he decided to bus people from the nearest Protection Camps, many of whom were mildly discontent with the Grace administration, in contrary to Stoly's advice.
During Grace's address, Stoly was near the President when he receives radio contact from Hale in seeing a sniper from the Ridley Hotel in which Stoly quickly hit Grace to the ground from being close to being assassinated, but only for the bullet to (non-fatally) hit the Governor of Colorado. After the attempted assassination on the President, Stoly later appeared in the secret base at Sheridon, Wisconsin where he expressed his frustration over the failure of Project Omega and Grace's death. During a moment of pause, Richard Blake spoke in contacting Vice President Harvey McCullen of his sudden succession which Stoly quietly accepts.