Hi, fairchess!
There are many books available for the so-called Modern Defence.
Since it is not cutting edge theory I think you can look even at some old books which are not outdated.
Such as the fantastic Jon Speelman & Neil McDonald's book - "Modern Defence" (Everyman Chess, 2000).
A little bit outdated, but really, really great is John Norwood's "Winning with The Modern" (Batsford, 1994).
Bogdan Lalic & Vladimir Okhotnik's "Carpathian Warrior" (V.Padiak Publishers) in two volumes (2005 & 2008) is maybe one of best opening books that never got the fame they deserved. Full of independent analyses! But not for beginners..
Books I never owned:
Nigel Davies - Starting Out, The Modern (Everyman Chess, 2008)
Andrew Martin's "Hippopotamus Rises, The Re-emergence of a chess opening" (Batsford, 2005)
...as well as many other books that treat Pirc & Modern in the same time..