Destroy the arcane focusing crystal tied to Magus Rimtori and then slay her. Afterwards, take the Head of Magus Rimtori to Ag'tor Bloodfist in Azshara.
A few more moments of thought brings a few ideas to mind, one of which brings a smile to your face: perhaps destroying the crystals would upset the blood elf responsible for the slaughter of so many orcs and the betrayal of Belgrom?
You continue to decipher more of the script and pictures and realize that one of the crystals is tied to the creator of the circle--the others are tied to something far more sinister.
You close the book and begin to decide which crystal to destroy.