Julia Alexander, managing a struggling art gallery, wants to save her marriage with Tony, a successful, but unfaithful plastic surgeon. The British ex-pats live luxuriously with their 10 year old daughter Isabelle in Spain. Julia is serious in her intentions and persuades Tony to take an intimate boat trip together - she also ends her affair with her lover Matthew. But her best laid plans backfire as young Isabelle secretly stows away on the yacht and during their voyage they encounter another yacht stranded at sea and decide to investigate.

A group of young urban explorers and a private military unit could become the final pieces in a 60-year plan to reopen a door that should have stayed closed. But what they unleashed could almost tear our world apart.