A veteran beat cop and teenage girl fall to their deaths from a tower block in south-east London, leaving a five-year-old boy and rookie PC Lizzie Griffiths on the roof, only for them to go missing. DS Sarah Collins is drafted in to investigate, working to find Lizzie before she comes to serious harm, but also to uncover the truth behind the grisly tower block deaths.

• Gemma Whelan
• Jimmy Akingbola
• Tahirah Sharif
• Emmett Scanlan
• Harriet Webb
• Karl Davies