James had decided to tag along. Because he could. Because he was bored. And well, to be honest (the real reason) was because Romana's concerns. Some days it was a complete balancing act, that involved juggling on your feet to gain James respect (let's not even touch on how difficult it was to regain his respect once lost) and on other days it was something as simple as procuring one of those muggle tapes that had the image of someone he decidedly didn't like being punch by a very tiny (though super-strong) woman. It didn't hurt that he'd thought her classy, in quite the McGonagall fashion from the get-go. And the fact that she didn't give him disapproving looks, STILL even though he'd long graduated, over her classes helped Romana's case a lot.
Quite honestly, at first, James hadn't seen what the big deal was. Muggles did dumb things for money all the time. And while, he never would have considered letting is uncle Ron go without back-up, it wasn't as if Alistair was running around loose anymore. His uncle could defend himself. Nevertheless, here James was, hand in his pocket. Wondering if he'd get paid just for showing up by someone. Because like hell would he have people poking about in his neuroses.
The thing was his uncle Ron didn't know that he was playing back-up. At least he didn't think he did. He had mentioned that he would tag along but he wasn't sure if his uncle had caught it. Or if he had even told his uncle. James was usually more put together for certain things, for things he deemed important ... back up for family was important, but lately his mind had been in SO many places. It was very likely that he had forgotten to inform Ron. Which was why he didn't startle his uncle with a 'boo'. After all at twenty-one James HAD managed to find maturity. Instead, he startled him with a rap not too far from Ron's head-he made sure to side step any coming limbs-and a, "I think the door is open. Might want to try it.