catch up with the in-crowd?

First, the indefinite article "an" is only ever used if it immediately precedes a word beginning with a vowel--so, you can be in an accident, but you cannot be in "an" traffice accident. That sentence should read: "In a traffic accident."

As for "catch up with the in crowd," the author is indulging ironic humor. The Prince, as a member of the royal family, represents the "in-crowd." The in-crowd meand those people who are most admired and emulated. This changes from group to group. For people who don't care about the royal family, none of its members are "the in-crowd." For people who do care about the in-crowd, who wish to seem more important because they know membes of the royal family, the Pricne would be a member of the in-crowd.

So, the author has "caught up with the in-crowd" in a very forcebul means, by being hit by the car with the Prince in it.

Let me make it more clear about the indefinite article "an."

We were in an accident.

The article "an" is used because if comes before a word (accident) which begins with a vowel.

We were in a traffic accident.

The article "a" is used because it comes before a word (traffic) which begins with a consonant.

"An" is only used because of the sound of the spoken language. If the word which comes after the article begins with a vowel, "an" is used to make clear that the two words are separate. If the word after the article begins with a consonant, "a" is used because the pronunciation is not needed to distinguish the two words. This is, perhaps, an archaic relict of the language, but i don't know anyone who doesn't use this, unless it were someone who immediately sounds uneducated by using the articles improperly.

Thank you Setanta!