It's the story of how Bilbo first got the ring. Also, I recommend the
Silmarillion, which has the story of the creation of Middle Earth, the history
of the elves, and the tales which are mentioned in LOTR (like Luthien and
Beren).
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~

Hey ho, to the bottle I go!
To heal my heart and drown my woe.
Rain may fall and wind may blow.
But there still be –
many miles to go!
Sweet is the sound of the pouring rain,
and the stream that falls from hill to plain.
Better than rain or rippling brook –
is a mug of beer inside this Took!