What surprised me the most wasn't the Rum reveal, but the fact that he's the same man from the old case where Camel messed up. I'll stop underestimating Gosho's ability to bring back seemingly irrelevant characters from ages ago. Hell, he might even bring Kichiemon Samizu back from the dead.
Anyway. Despite the FBI's recurrent silly mistakes, I thoroughly enjoyed this arc. Can't wait to see what Rum's next move will be.