Shetland - Season 4 Episode 1 -

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.