Many of the best fantastic stories begin in a leisurely way, set in commonplace surroundings, with exact, meticulous descriptions of an ordinary background, much as in a 'realistic' tale. Then a gradual - or it may be sometimes a shockingly abrupt - change becomes apparent, and the reader begins to realize that what is being described is alien to the world he is accustomed to, that something strange has crept or leapt into it. This strangeness changes the world permanently and fundamentally.