At the start of the Civil War, Dr. William McPheeters was a distinguished physician in St. Louis, conducting unprecedented public-health research, forging new medical standards, and organizing the state's first professional associations. But Missouri was a volatile border state. Under martial law, Union authorities kept close watch on known Confederate sympathizers. McPheeters was followed, arrested, threatened, and finally, in 1862, given an ultimatum: sign an oath of allegiance to the Union or go to federal prison. McPheeters "acted from principle" instead, fleeing by night to Confederate territory. He served as a surgeon under Gen. Sterling Price and his Missouri forces west of the Mississippi River, treating soldiers' diseases, malnutrition, and terrible battle wounds. From almost the moment of his departure, the doctor kept a diary. It was a pocket-size notebook which he made by folding sheets of pale blue writing paper in half and in which he wrote in miniature with his steel pen. It is the first known daily account by a Confederate medical officer in the Trans-Mississippi Department. It also tells his wife's story, which included harassment by Federal military officials, imprisonment in St. Louis, and banishment from Missouri with the couple's two small children. The journal appears here in its complete and original form, exactly as the doctor first wrote it, with the addition of the editors' full annotation and vivid introductions to each section.