Conversation so far:
who was put in the lion's den in the bible
Daniel was the biblical figure put in the lion's den.
who put Daniel in the lions' den?
Darius put Daniel in the lion's den.
what happens to Daniel in the lions' den?
God shuts up the mouths of the lions, and the next morning Darius rejoices to find him unharmed.

Question: what is the book about?
Self-contained rewrite: what is the book of daniel about?