First described as a “clumsy man deep in his books”[1], the chaplain is the resident clergyman at the villa. His name is never given. He seems to keep mostly to himself.
There are multiple references to him being a man who values books and reading highly. This, coupled with the fact that he only rarely approaches the Duchess about anything[2], contributes to his negative reaction to the Duchess's rebuttal of his request for money to acquire more volumes. Although he does not immediately react badly, the relationship between him and the Duchess is strained after this point.
The chaplain seems aware of what is hinted at to be going on between Ascanio and Duchess Violante below the chapel. He rushes through mass at a very fast pace; so as to escape the cold, the old man says, though also perhaps to escape the knowledge of what takes place in the crypt below. Between the lines, one may assume that the chaplain is spying on the Duchess; perhaps he is acting of his own volition to revenge himself upon Violante, perhaps he is acting on behest of the Duke, or perhaps both. The old man's grandmother happens upon the chaplain trying to peer into the chapel's window[3] and the chaplain stalls Nencia and the grandmother when they try to warn the Duchess of the Duke's arrival (relatively obviously feigning surprise).[4]
Whether his involvement is interpreted as petty or understandable by the reader, the chaplain, though he is quiet man and unassuming, is complicit in the demise of Ascanio and Violante, which makes him an accessory to murder.
[1] Wharton 1901, p. 8
[2] see Wharton 1901, p. 10
[3] see Wharton 1901, p. 11/12
[4] see Wharton 1901, p. 13/14