“How I Met Your Mother’s” Josh Radnor stars in the first full-scale PBS-produced miniseries in a long time, “Mercy Street,” the story of a Civil War hospital in Union-occupied Alexandria, Virginia.

As always happens in wartime, when there are vast numbers of injuries affecting young, healthy patients, there were enormous advances in medicine during the Civil War. In this hospital, there are nurses from both sides of the conflict, along with a black laborer (McKinley Belcher III) who is more knowledgeable about medical treatment than some of the staff, and a newly freed woman (L. Scott Caldwell).