What Walter had said in the morning was that Chief Nelson wanted them as temporary security guards for a private party.
The truth was that they had received official invitations as guests.
They wouldn't be copying secret agents in the movies and dressing up as waiters to hide their identities, nor would they be stepping out in formal suits like special agents.
They wouldn't be searching people at the entrance, or delivering alcohol on trays.
Selina hadn't thought much of the party at first, but Luke reminded her, "This is the first sort of official private party we're attending. You can wear one of the dresses you bought."
Selina's eyes lit up when she heard that.
She wasn't especially fond of lavish soirees or whatever, but she was very interested in attending an official dinner party in a formal gown. After all, this would be her first time.