How much of the epic do I need to have done to start the Black Book of Mordor?

[Hydranova]

So I've beat the four volumes of the main epic, but I've been playing a captain and solo gameplay is....a bit repetitive, so I'd like to level an alt up to 105 to pick up the BBoM. If I were to try and skip most of the epic, how much do I need to complete in order to be able to start BBoM? Do I just need to do the last few books of Vol 4, or something more substantial?

[Rylnconn]

show up at the wastes if your level 100 aragorn will get you started , then pass you off to Gandolf