Paul LeVal was a junior officer during the American Civil War. He was Will Johnson's South Carolinian cousin and fellow West Point alum. Pressed into CSA service against his will, he was openly opposed to the goals of the military in which he was forced to serve.
When his father got wind of his insubordination, he pulled strings and had him placed in the command of Colonel Jubal Eustace. A cruel officer tasked with catching runaway slaves, Eustace, it was hoped, would instil discipline in the younger LeVal. Although he rose to be Eustace's chief lieutenant, however, he never understood or accepted slavery — making his function in the CSA army both ironic and ultimately untenable. His mental state was severely impacted by the dichotomy of his position, and both Will and Will's fiancé Claire Bartlett actively worried about him. Fortunately, Will had met the Fifth Doctor by the end of the war, and the Doctor promised exceptionally effective therapies to help LeVal find his way back to mental health.
True to his word, the Doctor was able to restore LeVal.
The biggest difference was in his eyes. The dead look was nearly gone from them. Not completely. I could see that a little of it was still in there, but only a little.
Peri seemingly identified with LaVal. Both were, in a sense, victims of the cruel Colonel Jubal Eustace, and the evil he represented. By choosing to conduct LeVal's therapy with Peri around, he had helped her get over her war experiences, too. Seeing Eustace's lieutenant come back to good mental health helped her come to grips with the unmitigated cruelty she found in the American South and the fact that she had killed Eustace at close range. (PROSE: Blood and Hope)