When her shark-diving cage breaks off and sinks to the seabed, a first-time diver must resurface amidst a looming great white before her oxygen tank runs out. [In The Deep, 2016]

The IMDB entry describes the film as two sisters trapped in the cage . ?So here is my take with co-protagonists:

When their shark observation cage breaks off and sinks to the bottom, two sisters, first time divers, must?resurface amidst looming great whites before they run out of oxygen.
(29 words)

Meant to be in Classics*