Alice was getting very tired of sitting by her sister on the bank, and of having nothing to do. And then the dragons arrived.

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. And then the dragons arrived.

The story so far: in the beginning the Universe was created. And then the dragons arrived.

Off you go, Spot!
Don't get lost.
And then the dragons arrived.
Spot's First Walk, Eric Hill, pub. Frederick Warne, ISBN 0 7232 5706 X

One day when Pooh Bear had nothing to do, he thought he would do something, so he went round to Piglet's house to see what Piglet was doing. And then the dragons arrived.
The House at Pooh Corner, A.A. Milne.