The Space Pirates

Now, they aren't really space pirates, but it's easier to think of them as such rather than trans-universal pirates. They are the scourge of the Multiverse. They travel from one universe to another, destroying and stealing as they wish, and then leaving before anyone has time to really get what's happening.
One fine morning in Bristol, they encounter a boy who loves pirates, but when he joins them, he finds out piracy isn't all the fun and games it seemed to be in books.