What puzzled me reading this is the indefinite article with "first".They [cops] ain’t never done a boat [a bust on a boat] before.
High-rise heroin mills, shotgun-house crack emporiums, biker clubs, gang corners—they done all that, countless times.
But a cargo boat?
That’s a first.
It's not that I didn't know that when an ordinal numeral is not used to order things but has the meaning "one more/ (yet) another", the noun it modifies is used with the indefinite article. However, the "a" article being used with "first" - unless it's in a set phrase like a first night or a first prize - is something I can't grasp.
It seems I missed some subtle point when reading about the articles and can't figure out now what it was.
Or was it just used to follow the freewheeling, colloquial style of the entire narration?
Or maybe there's no issue concerning the grammar to be paid any, much less close attention to? :-)