An Irish detective stumbles upon some valuables that might be connected to a terrorist plot.

With the discovery that another bombing is imminent, Emer and Christian's attention is drawn to a well-known Irish businessman with a very chequered past.

Rough diamonds are found in Fionn's offices; Emer links this evidence to the bombings and warns Fionn that his life is in danger; Christian discovers that one of Sana's friends has been beaten by a fellow officer.

As the search for Fionn begins, Christian suggests that Fionn's frequent travels to Surat, India, may point to a diamond connection.

While her team follows the money trail in Ireland, Emer and Christian discover the real identity of the bombers; a very unexpected source provides the investigation with invaluable information.

With someone now in custody, Emer and Christian face a desperate race against time to stop the final bombing and uncover who was really behind the terrorist campaign.