France's Périgord region is the proud home of the famed black truffle, the 'Black Diamond'. Yet reports are coming in that this treasured asset is being adulterated with an inferior Chinese substitute, affecting the value of the genuine article. Chief of Police Bruno Courrèges is called in to investigate.

Meanwhile, tension is brewing in Saint Denis. A Vietnamese market stall has been vandalized by a Chinese gang, leaving inter-country relations at breaking point. Then, as if to prove that bad things come in threes, murder rears its ugly head. Bruno can't help but wonder if these problems are connected.

When his suspicions are confirmed, Bruno finds himself facing a very present danger, one brought about by a long-buried feud tracing all the way back to France's colonial past.