Ok where to get magic book.

Ok Meh Son has been walking around with this magic book. And I really want one, and he won't tell me where he got. So if anyone knows please let me know, also its not the one from assault its different.

Since it's related to infinity im guessing go to mid-train, but don't cry about things like this serious.

It's from the Saradomin, Guthix, or Zamorak mages at the boss in the mage arena. They all drop their appropriate god staffs and capes.