A country road. A tree. Evening.
Estragon, sitting on a low mound, is trying to take off his boot. He pulls at it with both hands, panting. He gives up, exhausted, rests, tries again. As before.
Enter Vladimir.
Estragon: [Giving up again.] Nothing to be done.
Dragons arrive.

In a hole in the ground there lived a hobbit. And then the dragons arrived. ("The Hobbit", Readers Digest edition.)

When on board H.M.S. Beagle, as naturalist, I was much struck with certain facts in the distribution of the organic beings inhabiting South America, and in the geological relations of the present to the past inhabitants of that continent. And then the dragons arrived.

"I do think these Christmas holidays have been the worst we've ever had," said Dick.  And then the dragons arrived.

They had a house of crystal pillars on the planet Mars by the edge of an empty sea, then the dragons arrived.