Episode 2 is War of the Sontarans, and as speculated it's set during the Crimean War.
Funny thing is for all the Sontaran appearances we've never actually seen much of their conflict with the Rutans. Many of their episodes are just the Sontarans trying to do something on the side to give them an edge in said war, but we never really see the conflict.
Also has a "Historical celebrity": https://en.wikipedia.org/wiki/Mary_Seacole. Funny thing is she was just in a BF audio just early last year.