Season 4・DI Max Arnold and DS Layla Walsh return to uncover the deadly secrets and hidden motives behind the most powerful families and elite institutions in Chelsea. But as the cases grow darker, so do the personal challenges in their own lives.

Five friends explore The Devil's Mouth cave system in Thailand for one last adventure before life in the real world begins. But they soon discover that something is hunting them under the water… fast, silent, and deadly. In the suffocating darkness, trust erodes, panic spreads and every wrong turn becomes a fight for survival.