Invisible Murder (Nina Borg Series #2)

The second installment in the bestselling Danish crime series starring Red Cross nurse Nina Borg, following Fall 2011's New York Times–bestselling The Boy in the Suitcase
 
In the ruins of an abandoned Soviet military hospital in northern Hungary, two impoverished Roma boys are scavenging for old supplies or weapons to sell on the black market when they stumble upon something more valuable than they ever could have anticipated. The resulting chain of events threatens to blow the lives of a frightening number of people.

Meanwhile, in Denmark, Red Cross nurse Nina Borg puts her life and family on the line when she tries to treat a group of Hungarian Gypsies who are living illegally in a Copenhagen garage. What are they hiding, and what is making them so sick? Nina is about to learn how high the stakes are among the desperate and the deadly.