Adam had caught the house staff on their way out. She had called ahead and told them to take the weekend off. In fact, Angela didn't even notice that they hadn't gone yet. As far as she knew she was completely alone in the house. But they had picked up her discarded clothing and put it in the laundry room as well as letting Adam through the door before they actually left. So not only was Angela unaware, but she was caught completely off-guard by Adam's presence.
Turning around quickly, startled at the sound of someone's voice Angela's eyes were wide. "Adam?" For a second she just stood there in nothing but a silken tank and her skirt slip and grey heels. And then she realized that she was wearing nothing and her eyes got even wider. "Adam!" Angela stepped as close to the fridge as possible and tried to close the door between them. To at least show some sort of decency.
"Not that it's not normally great to see you but... what are you doing here? You know Arthur's in Vegas with Daniel, right?" It wasn't completely unheard of for Angela to spend time with Adam. In fact, she rather enjoyed time spent just the two of them. But being startled as she was, feeling a wee bit exposed, she had responded a little bit on the defensive.