This is a story about two con men in British Imperial India who cook up a scheme to make themselves kings in Afghanistan. One of Kipling's better short stories, it was admired by writers as disparate as J.M. Barrie and H.G. Wells. It suffers a little from having had a zillion imitators in the intervening century or so, and like a lot of Kipling's works, there's an undertone of paternalistic imperialism that modern readers may find grating, but it isn't like he's showing the British in a positive light either -- this is Kipling at his best, and at his best he was too good a writer to let anyone, including the British, off the hook.
Read this if you're trying to figure out whether or not you like Kipling's works that are aimed for adults -- it's very different in tone from, say, The Jungle Book or _Just So Stories_, which were written for children. If you like this, I recommend you grab Plain Tales from the Hills, his first collection of stories set in British India; it should also be available online for free.
If you're interested in the historical background for this story, it was at least partially inspired by a real individual, an American named Josiah Harlan.