When Nicola returns from taking her daughter to school to discover that her 52-year-old husband Mark has left the house, she immediately calls the police. The simple fact that he has gone out rings alarm bells, and even worse, he has left behind a worrying note saying he needs to ‘seek revenge'. When officers from South Yorkshire Police attend the scene, Nicola discloses that she thinks Mark's pocket knife is missing too.
Nicola is worried about Mark's mental health, which has recently deteriorated. He has suffered from PTSD ever since he was assaulted a few years ago, and in recent weeks he has gone missing several times. Mark's note states that he's heading to a street in Sheffield where he believes his attackers are based. Nicola also reveals to the police that Mark often heads to the Sheffield Canal, the place where he was attacked. Officers need to mount an intensive search of the canal, which is over four miles long, in the hope of finding Mark before it's too late.
Across the city in Ecclesfield, police receive a call about a woman who may be at risk of harming herself. Her son has woken up to find she has vanished from their house and posted her keys back through the letterbox. What makes it so alarming is that she never leaves home. She suffers from anxiety and depression and has spent the past 12 months shielding due to the Covid-19 pandemic.
Upon discovering that she has previously attempted suicide, Inspector Matt Wood immediately classifies the case as high-risk. Concern mounts when officers at the family home discover that a quantity of the woman's medication may be missing. A potential CCTV lead proves a dead end, but the woman's phone data results present a worrying new possibility about where she may be.
