Book that's brutal, no less (4)

I believe the answer is:

ruth

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'book' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for ruth that I've seen before include "Lady" , "she married Boaz!" , "She is followed by Samuel" , "- - Rendell, crime writer" , "Biblical woman" .)

I've seen this clue in The Independent.

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