Sin'dorei Tome of Summoning

Bring the Sin'dorei Tome of Summoning to Zevrost in Orgrimmar.

You were wise to take this, <name>. More than killing Rimtori, keeping this out of the blood elves' hands will ensure they are powerless to retaliate against us.

As for deciphering the tome itself, I have a contact in Orgrimmar who dabbles in such things--a warlock named Zevrost. He can be found in the Cleft of Shadow.