Jean hadn't particularly expected to ever be the active Watcher.
He hadn't particularly expected not to, either; but the average Watcher sees ten Slayers called during his tenure, and there are hundreds of Watchers serving at any given time. The odds, even for a Watcher of outstanding merit, are slim.
The form letter comes from the Council when the Slayer dies -- a girl in Tokyo, seventeen, stopped an apocalypse but bled out doing it -- notifying all the Watchers; it's black-edged, formally worded, on stiff paper, and a week late, because he lives across the Atlantic from headquarters. (The Council still isn't really comfortable with phones, let alone the internet. At least the letters are Xeroxed, now, not hand-lettered by grumbling Watchers-in-training.)
The follow-up letter, informing him that the new Slayer has been Called and located, is Xeroxed, too, but the enclosed slip is in hand-drawn calligraphy. Jean is close; Jean is qualified; Jean is not occupied with anything from which he cannot be spared. Jean is to be her Watcher.
Jean writes back a correctly worded acceptance, and phones Resources to let them know what he needs. He'll have a conveniently flexible lecturing position at the local university, and approval to start a very exclusive enrichment program at the local school, and an unremarkable little apartment chosen chiefly for defensibility. Other arrangements he handles himself: wards on his new apartment, suitable adjustments to the style of his wardrobe, purchases of training equipment billable to the Council.
When he knocks on the door corresponding to the Slayer's address, he's dressed, coiffed, and ready for his role: actor of some small note, entirely professional, perhaps a little bored, here on a matter of business. A little too well-dressed to be a door-to-door salesman, a little too much attention to fashion in the cut of his suit to be a threat. Too pretty, and too familiar with the most upper-middle-class artistic sort of ennui, to be concealing any sort of hidden depths.