Begins with statistics. 3000 people are in witness protection and the officers who run the cases themselves have to have aliases. Their department has to be separate from any other police department.
Siobhan Finneran is assigned to a WP family that is wiped out by hit men, and her colleague (Barry Ward) is also shot. But there's two problems with that. 1. He's not working on that case and shouldn't even know where the family is. 2. He is married but they are having an affair. The survivor, a little girl, knows something but is not telling and that puts her in danger from crime boss Alec Newman. So lots of good conflict.
And there's more conflict from investigating police Nadine Marshall and Katherine Kelly (Mr Bates vs the Post Office, The Long Shadow, Gentleman Jack). Chaneil Kular is her No. 2. Andrew Knott is a helpful DI, David Hayman is the father in deteriorating health, Nichola Burley is the cheated-on wife.
Siobhan we know from as far back as Rita, Sue and Bob Too, her debut, in 1987. Then lots of TV, notably Clocking Off (2000-02), Boy A (2007), Downton Abbey (2010-12), The Syndicate (2013), The Selfish Giant (2013), Cold Feet (2017-19), Happy Valley (2014-2023), Time (2021-23) and Alma's Not Normal (2021-24).
Mrksa is the creator but it's 'inspired' from an idea by Gary Madden, and there are co-writers in the shape of Polly Buckel and Giulia Sandler. A six-parter for ITV.