It's the launch day for the Institute's new submersible and Ellis is keen to show off his hard work. But when faulty programming accidentally launches the sub into the ocean, Taylor, Ellis and Meesha are trapped below the depths.

The group are in a desperate race against Raquel to the energy source. But with Taylor wracked by disturbing visions, tremors erupting across the island and an emergency evacuation declared, has the situation finally become too much for the gang?