For those wondering what PBS is planning to do once “Downton Abbey” wraps up its final season in 2016, it appears the network is getting help from a very unlikely source. Former “How I Met Your Mother” star Josh Radnor has signed on for "Mercy Street," a six-part drama series about the Civil War.

Radnor joins Mary Elizabeth Winstead, Gary Cole and newcomer Hannah James. This provocative story focuses on a group of doctors and nurses living in the city of Alexandria, Virginia during its occupation by the Union army in the 1860s.

According to Variety, the story follows two nurses on opposing sides of the abolition debate, brought together to work in a Union-controlled hospital. Mary Phinney (Winstead) is an abolitionist who comes to the family home of Emma Green (James). The Greens owned a hotel that was converted to a hospital after the city’s occupation. The show is inspired by memoirs and letters from real doctors and nurses that volunteered at the actual Mansion House Hospital during the Civil War.

Radnor, in his first role since ending his nine-year run as the star of CBS’ popular sitcom “How I Met Your Mother” in 2014, will play Jedediah Foster. According to The Wrap, Jedediah is a civilian contract surgeon who grew up in a privileged, southern and slave-owning household. He’s the son of a wealthy land owner in Maryland and makes his way to the household to work on troops. However, given his background it is unclear how he will feel about patching up Union troops.

Also rounding out the cast is: Peter Gerety, Norbert Leo Butz, Jack Falahee, and AnnaSophia Robb, McKinley Belcher III, Shalita Grant, Cherry Jones, Cameron Monaghan, Donna Murphy, Tara Summers, L. Scott Caldwell, Suzanne Bertish, Wade Williams, Luke Macfarlane and Brad Koed. The series will be executive produced by famed producer and director Ridley Scott.

“Mercy Street” will air Sundays in 2016 alongside episodes of the final season of “Downton Abbey.”