Criminal Minds2005

“It cannot be seen, cannot be felt.

Cannot be heard, cannot be smelt.

It lies behind stars and under hills,

and empty holes it fills.

It comes first and follows after.

Ends life, kills laughter.”

The answer is dark; the dark, dark

(Gollum's Riddle is a song whose score was written by Maury Laws for the 1977 film adaptation of the The Hobbit. It follows the riddle Gollum proposes to Bilbo until the ending line)

But like many endings, Spenser quotes this from Tolkien at the end of one of the episodes. I believe it is the episodes where he gets released from prison.