Supernatural Heart of the Dragon by Keith R.A. DeCandido

A Supernatural novel that reveals a previously unseen adventure for the Winchester brothers, from the hit CW series!

When renegade angel Castiel alerts Sam and Dean to a series of particularly brutal killings in San Francisco's Chinatown, they realise the Heart of the Dragon, an ancient evil of unspeakable power, is back! John Winchester faced the terrifying spirit 20 years ago, and the Campbell family fought it 20 years before that - can the boys succeed where their parents and grandparents failed?