FanPyre,
You're correct in saying that the Heretic's Key that Kol gives you unlocks the area where the statue of Kerah is, but Sazerac is yet more correct in that the Tome of Fire is not anywhere near Kerah's statue, but back in the maze after you kill the naga. You will need the skull key off the Serpent Master to open that area.
AliCat
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