Garda Sergeant Jack Driscoll (Owen McDonnell) is back in action, this time in a new six part series. In the fourth series of this hugely popular and acclaimed drama serial childhood friendships, family ties, and romantic relationships are all tested to the limit. Some of the incidents which Jack must resolve include the violent death of a reclusive old man, an arson attack on a housing development, and a mysterious car crash, all of which draw him into dark and personally dangerous territory, as he has to probe the grey area between human failings and criminalit. Jack's personal life is complicated with the arrival of Brian (Matthew McNulty), an English cousin, who's visiting with his girlfriend, Gemma (Simone Lahbib). Brian's search for the father who abandoned him as a child opens old wounds for Eithne (Ruth McCabe) as a heartbreaking family secret is revealed.