A lot of Saki's stories are set during the Edwardian Era in England (1901- 1910), and mock the social conventions of the period, as well as the hypocritical behaviour of the middle and upper classes. In some ways, his works can be compared to PG Wodehouse's: funny social commentary, and frequently featuring a well-born, single young man of fortune- either Clovis or Reginald- at various societal functions, such as the house party in Tobermory . But while Wodehouse's Bertie is a hapless and frequently innocent victim of friends, acquaintances, and relatives, Clovis- or Reginald- takes great delight in discomfiting and deflating the pretensions of the people in his social circles. Saki is sort of Wodehouse with a tinge of maliciousness, an edge of cruel irony.
Tobermory is the truth-teller in this story. A teller of unpalatable truth perhaps, but truth nonetheless. Not that Tobermory's honesty is a sign of virtue; cat-like, he simply is indifferent to the feelings of others. Tobermory is the observer who sees all the dishonest, hypocritical and dishonourable behaviours practiced by this group of "nobles". He tears the polite veil off of their reprehensible actions, exposing them for what they are. It's of course amusing and satisfying to see pompous hypocrites brought down a peg, but there is a serious point being made behind the humour.
There have been countless examples throughout history where people, instead of becoming angry over wrongs or injustices being done, have instead bitterly attacked those who exposed them to the truth. And I can think of at least one contemporary, ongoing issue where we see this occurring- one side preferring to keep what they're doing swaddled in polite euphemism, their supporters refusing to even look at evidence which casts them in a bad light. They don't attempt to persuade or debate, but rather seek to shut up those who are so vulgar as to point out things which make them uncomfortable. When did this cowardly and hypocritical response to challenge become O.K.? Why isn't our first response to such statements, "Is it true?" rather than, "How can I stop this from being said?" Why? Because looking straight at something we've done- or allowed to be done- instead of averting our eyes might mean having to acknowledge wrongdoing and then do something about it. And no one wants that, do they.