"A Dissertation Upon Second Fiddles", first published in 1902 is a collection of four, slightly interconnected, stories.

O'Sullivan's characters flit between the stories, all of which have a slightly moralistic purpose. However, O'Sullivan's macabre sense of humour ensures that the tales do not preach, and he puts his black wit to good use in this hard-to-find collection.

"Of Kindred" describes a mysterious German stranger proffering advice to the large and corpulent Sir Hugh Anger so that he can resolve his hypochondria and live a longer, healthier life.
"Of Accomplices" is the story of Shawlcoat Vellery, a good and virtuous man, who rather bored with his righteousness, comes across the anarchical and nihilistic Labour Argan. Vellery decides to act as Argan's henchman in various schemes but the results are not as anticipated.
"Of Friends" describes Nicolas and his wife Hester. The pompous Nicolas is persuaded to make a speech for a local politician but it ends disastrously when Nicolas is attacked and beaten by ruffians. While Nicolas is recovering in bed, the MP, a portly gentleman of some 50 years, who has admired Nicolas's russet-haired wife with her "strong white neck, and the perfect and most pleasing harmony of her whole frame", takes his chance to try "to beat down the guard" of the unfortunate Hester.
"Of Enemies" is the tale of a flighty, yet pretty, novelist, Mrs Ardour, who comes across a short story in an obscure magazine. She decides to steal the plot and sets on writing a novel based on the story. When the original writer discovers this plagiarism, Mrs Ardour uses all her skills and wiles to ruin him completely.