Once Burned — Peter David

There's a bar called "The Captain's Table," where those who have commanded mighty vessels of every shape and era can meet, relax, and share a friendly drink or two with others of their calling. Sometimes a brawl may break out but it's all in the family, more or less. Just remember, the first round of drinks is always paid for with a story...even in Thallonian space.
Six years ago, long before he took command of the Starship Excalibur, a young Starfleet officer named Mackenzie Calhoun served as first officer aboard the U.S.S. Grissom. Then disaster struck, and Calhoun took the blame. A court-martial led to his own angry resignation from Starfleet...or so it appeared. At long last Captain Calhoun reveals the true story behind the greatest tragedy of his life.