There are implications plastered throughout the book that Ser Maynard Plumm is Bloodraven:
Dunk says that Maynard's facial features are hard to pin down, which sounds a lot like a description of glamour in A Dance With Dragons.
In another scene, someone quips, "If that were true, we'd all be bastard sons of old King Aegon," to which Plumm responds, "Who says we aren't?"
When Kyle begins to blame Bloodraven for not doing anything to stop the Ironborns, Maynard immediately interjects that Bloodraven is keeping all of the ships in King's Landing in case the Blackfyres invade from Tyrosh. How strange it is for a simple hedge knight to know exactly what the Hand of the King is planning.
When Glendon pours his wine to the floor in response to a toast to Bloodraven, Maynard quips, "A sad waste of good wine." The man is likely a little sad that people would rather waste good wine than drink to him.
Bloodraven is absolutely terrifying when you think about it. He nipped the rebellion in the bud by being aware of the plot at least a week in advance, if not more. Westeros is quasi-medieval word. The way to plot things is either via ravens and messages (which leave evidence and is slow) or by meeting in person, which is also risky and slow. The plots generally go with the following order of things: meet with like-minded people and drum up support, plan, call your levies, war! Bloodraven called an army several thousand strong while the plotting lords were stuck with just their bodyguards (a few fighters, because they were going to wedding and not battle), because they were still on step one while he was on step three. Again, summoning levies takes time.
Even though Aerion deserves it, Egg is fully on board with Daeron's suggestion for Dunk to kill Aerion during the Trial by Seven. He's only 10, yet he's already willing to break Westeros' biggest taboo of kinslaying.
