Jacob/Peter
A party like this was about the last thing in the world that Jacob would have gone to on his own - but seeing as he lived here, and he was fairly sure Marlene would track him down if he had tried to hide, Jacob was out and about at the party. It was loud and so far over the top that the top couldn't even be seen any longer.
And the company left something to be desired, there were far too few Slytherins a part of the Order - or far too many Gryffindors in any case. Jacob mostly kept to himself, drink in hand and scowled at anyone who even seemed like they were going to try and talk to him. It was enough that he was there with all of them, he didn't need to be subjected to whatever it was any of them wanted to talk about as well.
Of course eventually he found Peter, watching him from across the garden for several minutes, until he caught his eye and motioned Peter over with just a slight tilt of his head, a small smirk on his lips.