Death of a Hollow Man, S1E3.

Filmed in Amersham, Buckinghamshire; Corn Exchange, Wallingford, Oxfordshire; Gerrad's Cross, Buckinghamshire; Harefield, London; Latimer, Buckinghamshire; The Lee, Buckinghamshire; and Wallingford, Oxfordshire (as Causton), S1E3, "Death of a Hollow Man," is set for the most part in a theater in Causton. 

Interiors

Commentary:

I found the tame and quiet plot a relief from the absurd and graphic murders in the earlier episodes. There is a terrible razor blade incident though, and it's Joyce's first exposure to murder. She is traumatized, but as we'll see in later episodes, she gets more familiar with it eventually. 

Cully meets Troy for the first time and says "This is not the theater," (which seemed a bit pretentious!). A nice bit is when Troy actually gets some praise (instead of mockery) from Tom for his input into the case. A minor story line about a gay couple, a bit of skin shown, an adulterous affair, greed, pride, theft, and of course, murder feature in this episode. Ignore all that nasty business and you're left with the wholesome warmth of Barnaby's home life to make it worth the view.

NEXT Episode, S1E3, "Faithful Unto Death."