When Shetlander Thomas Malone has his murder conviction overturned after 23 years, which he's spent behind bars, Perez has to reopen an investigation into the 1994 death of local teenager Lizzie Kilmuir. Later, Perez gets a text from Cassie saying she is unexpectedly flying back to Shetland, so he and Duncan meet her at the airport.
When a young archaeologist discovers a set of human remains, the Shetland community is intrigued to know if it's an ancient find or a contemporary mystery. And when an elderly woman is shot on her land in a tragic accident, Perez and his team find themselves at the centre of two feuding families whose envy, greed and bitterness has divided the surrounding community.
Shetland - Series 4, Episode 1 Synopsis and Schedule