As a Starfleet officer, Calhoun served aboard the USS "Grissom", where he meets Katarina "Kat" Mueller, who would become his lover. It was on the "Grissom" that he learns to play poker, and establishes a reputation for being able to bluff his way through any hand, even evading an empath's attempt to get a bead on him. Calhoun was present during a catastrophic event aboard the "Grissom", which led to his apparent departure from Starfleet. In reality, he becomes an undercover operative for head of Starfleet Intelligence Admiral Alynna Nechayev who, years afterward, fearing Calhoun was getting "too deep" into the lifestyle of the thugs and criminals he was associating with, pulled him out and gave him his own starship to command, the USS "Excalibur". It was in taking this command that he is reunited with both Shelby, who was now his First Officer, and Mueller, whom he picked as his Executive Officer (the terms are normally synonymous on the various television series, but in the "New Frontier" novels, a First Officer heads the ship's day shift, while the Executive Officer commands the night shift watch). Calhoun is assigned to Sector 221-G, the area of space of the former Thallonian Empire, which has collapsed, resulting in destabilization of the region.