What would be an introduction to "The Gardener"?

You would want to write an introduction that first, gives a little historical background to help the reader understand the story; second, provides an overview of the story; and third, mentions the tone of the work, so the reader has some idea of what to expect. You don't want to give away the whole story.
You might say something like the following: Kipling's story has an ironic tone as it deals with the death of Michael and Helen's response to the death. It was written in 1925 after Kipling visited a World War I graveyard in Rouen, France. Some of the chaos of war and death comes across in this tale written close to a century ago.
This kind of introduction mentions the tone of the story, gives some historical background, and says a little about the plot without giving away the story. You could also look up information on Kipling and include that. You will probably want to expand this a bit.