Look at this two examples from J.K. Rowling's "Harry Potter and the Deathly Hallows", Bloomsbury Publishing Plc, 2007, chapter I, p.9

1. (the very first sentence) The two men appeared out of nowhere, a few yards apart in the narrow moonlight lane".
We don't know anything who were the men and where the lane was. Why is the definite article used in the both occurences?

2. The lane was bordered on the left by wild, low-growing brambles, on the right by a high, neatly manicured hedge. [...]The high hedge curved with them, running off into the distance beyond the pair off impressive wrought-iron gates barring the men's way.
Why "THE" pair of gates? We read about them for the first time.