Hayley Atwell reprises her role as Carter from the film series, and is joined by regular cast members James D'Arcy, Chad Michael Murray, Enver Gjokaj, and Shea Whigham.
In January 2015, Marvel announced that the sixth episode would be titled "A Sin to Err", to be written by Lindsey Allen, with Stephen Williams directing.
[1] In January 2015, Marvel revealed that main cast members Hayley Atwell, James D'Arcy, Chad Michael Murray, Enver Gjokaj, and Shea Whigham would star as Peggy Carter, Edwin Jarvis, Jack Thompson, Daniel Sousa, and Roger Dooley, respectively.
[1] It was also revealed that the guest cast for the episode would include Lyndsy Fonseca as Angie Martinelli, Alexander Carroll as Agent Yauch, Ralph Brown as Dr. Ivchenko, Meagen Fay as Miriam Fry, Bridget Regan as Dottie Underwood, Devin Ratray as Sheldon McFee, Steven Hack as Albert, Rick Peters as Dr. Honicky, Dimiter D. Marinov as Fyodor, Dave Matos as Pasha, Victoria Profeta as Josephine, Yasmine Aker as Thelma, Krista Marie Yu as Edith, Kellen Michael as Small Boy, Joyce Greenleaf as Esther, Mike Massa as SSR Agent #1, Marcus Young as SSR Agent #2, and Denney Pierce as SSR Agent #3.
[1] However, Carroll, Matos, Profeta, Aker, Yu, Michael, Greenleaf, Massa, Young, and Pierce did not receive guest star credit in the episode.