Night shift supervisor, Karsen, sends four divers, Engel, Mitchell, Jones and Hurst, down in the diving bell to fix a damaged oil pipe.

Having completed the work they make the ascent but the support ship is hit by a storm, causing the cables holding the bell to break.

The four men then have to use their wits and knowledge of diving and the bell to try and escape from the ocean floor, 670 feet (200 m) down, with a limited oxygen supply.

Engel chooses to sacrifice himself to save Jones, sharing a story of how his selfishness in the past cost a young boy his life.

Though Jones develops bleeding from the mouth due to decompression sickness given his fast ascent, he reaches the surface and is rescued by teams from the Marlborough.

"[4] Conversely, Jeremy Aspinall of the Radio Times commented, "It's perfectly watchable, if not quite on a nerve-shredding par with lung-busting thrillers like The Poseidon Adventure, The Abyss or Black Sea.