Andromeda wasn't surprised that he gave his word. She had grown up in a house of Slytherin's and she was clever enough to know that was good for him but at the same time good for her too so of course he wouldn't go back on his word. He wanted something from her after all and the only way to get that would be if she co-operated.
"Deal," she said simply. Though she agreed to this it didn't mean that she diodn't have a plan of her own up her sleeve if something went awry or the like. She would still be just as cautious, if not more than if he hand't given his word. If he hadn't well she would have known that he was up to something but now she didn't have that. Still it payed to be careful after all. "Lead the way then."