The thriller, based on the novels In The Woods and The Likeness by author Tana French, sees two detectives investigating the murder of a young ballerina, and a second murder that becomes linked to the crime.
The series is set in 2006 and follows Detective Rob Reilly and his partner Cassie Maddox as they investigate a child murder in a local woods.
However, this is not the first time a child has gone missing in the area of Knockaree. In the 1980s, three children disappeared but only one came back alive and the people of Ireland and particularly Rob and Cassie worry the cases may be linked.
New on BBC One.