Shetland BBC1, 9pm

As Perez (Douglas Henshall, below) and his team search for the link between two deaths, the return of convicted murderer Donna Killick is also sending shockwaves through the community. She’s been released on compassionate grounds due to her terminal illness, but her victim’s sister, Kate Kilmuir, isn’t feeling that kindly towards her – and Perez is also unnerved by Killick’s apparent lack of remorse for her crimes. ★★★★★