There’s a slick little line in Indian Summer which is almost a primer on good writing. It’s towards the beginning of the episode, when Don first walks into the office, he says, “Peggy, will you bring me a glass of ice water? Someone forgot to tell the sun it’s October.”

That line
(a) Establishes that it’s a heat wave, which is a major theme of the episode.
(b) Establishes Don. It is exactly his voice, his wit, his style of speech. If you’ve never seen the show before, you know a little something about Don from hearing his opening line. Furthermore, Don is unfailingly polite to Peggy, he never says “bring me,” only “will you bring me” or “please bring me.” Plus, Don is so much a boss that the heat is someone’s forgetfulness. It’s the language of a man in charge, directing the world to his will.
(c) Brings Peggy into the office just a couple of minutes later (presumably she had to go somewhere for ice) so that they can realize she’s the right person for the Relaxiciser account.

In one line. Brilliant.