Episode 1

When 16-year-old Larissa’s mother Karen calls the police, it is to report that her daughter has run away after an argument at home. But what initially sounds like a typical teenage scenario becomes a major missing persons investigation when Karen reveals that Larissa has bipolar disorder and that she has left home in her pyjamas.

At Pollok Police Station in Glasgow, Seargeant Ross Kelly swiftly tries to call Larissa’s phone - but there is no reply. He tasks officers with scouring the local area to see if they can spot her quickly. Meanwhile, mother Karen waits anxiously at home.

Police are tipped off that Larissa may have headed to Rouken Glen, a vast country park just 20 minutes from her house and where she was found during a previous bipolar episode. While teams of officers divide up to scour the park’s woodlands and waterways, Karen discovers that Larissa has taken over £200 in cash from home, prompting Seargeant Kelly to widen the search across Glasgow. But as darkness falls, and with Larissa missing for nearly four hours, no-one knows how far she may have travelled. Larissa has been in the care of mental health services since the age of five, with family tragedies compounding her struggles.

The following morning, Larissa is still missing and has potentially been outside all night, missing vital medication. Her case is now classed as high risk, but attempts at tracing her phone only result in another dead end. Karen is already fearing the worst has happened when routine police custody and hospital checks make a devastating discovery.

In Edinburgh, PC Andy Porteous has noticed a change in the mental health of many of the young people who are reported missing. He is on duty when another anxious mother reports to police that her son Bobby has failed to return home overnight, after being discharged from hospital the day before. As Bobby is 18, PC Porteous needs to find out from the mother whether Bobby has simply chosen not to come home, or whether it is for more concerning reasons.

Bobby’s mum reveals that he has previously made multiple attempts on his life, and she thinks that his self-harming is escalating again. Officers search places where Bobby has been found during previous mental health episodes, and while the city’s CCTV operators quickly flag a potential sighting, it turns out to be false. With growing fears for Bobby's safety, police gain access to his financial records and discover that he has been sending money to a friend. But although this might be proof of life, it leads to another dead end, and police still don’t know whether Bobby is intending to harm himself.

As further financial tracking finally gives police a vital breakthrough and enables them to track Bobby in real time, they make a new, worrying discovery - he is apparently heading towards the coast and maybe into the sea. Teams race to intercept him in a last-ditch attempt at saving his life, but will they make it in time?