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Grognak the Barbarian on a table sitting on some rubble to the east of the hallway leading to the Vernon Square North exit. Height-wise, it's halfway down to the platform, directly next to the concrete bench; a board leads over the railing from the upper level, and there is a table with a lamp on it. You have to jump down onto the rubble to get to the table. If the book is not on the table, look at the very bottom of the rubble on the floor.