Erik heard midnight, and so he arrives at midnight, desiring neither to be fashionably late nor to waste time hanging around just for the sake of it. (If he wanted to attend a party, he'd bloody well attend a party.) He'll probably end up hanging around anyway, because people are often slow to congregate, but oh well. There are worse stereotypes to fulfill than punctuality.

Presumably, as suggested, he arrives with an extra body or two—although John, unlike Charles, will have been left to his own devices in regards to showing up, so who knows if they'll all arrive together.

He looks slim and serious, as is the norm, smartly but casually dressed. No work boots this time.