NEW YORK – There's blood in the water in the shark-themed thriller "47 Meters Down: Uncaged" (Entertainment Studios).

Crafting a jumpy follow-up to his 2017 original, returning director and co-writer (once again with Ernest Riera) Johannes Roberts ramps up the gore but also explores themes of altruism, cooperation and family unity on the way to a coincidental ending that strains credulity.

The spectacle of lovely young bikini-clad ladies in peril having proved profitable the first time out (who'd have guessed?), Roberts doubles their number from the two sisters we followed in the first movie to a quartet of American teens living in Mexico. Like the south-of-the-border setting, the sibling pattern remains, however, since two of the four are quarreling stepsisters Mia (Sophie Nelisse) and Sasha (Corinne Foxx).

Mia is an outcast at school while Sasha is popular and hangs out with the cool crowd, which includes devoted thrill-seekers Nicole (Sistine Stallone) and Alexa (Brianne Tju). Unfortunately for all concerned, the latter duo convinces Mia and Sasha to substitute scuba diving for the glass-bottom boat tour their archeologist dad, Grant (John Corbett), had arranged as a means of enabling them to spend quality time together.

Worse yet, their chosen venue is the submerged Mayan city Grant has been exploring and which the script has already established as being shark-infested. Before you can shout "great white," parts of these ruins have collapsed, trapping the rash girls in cozy proximity with a pack of predators. And, of course, their limited supply of oxygen is another potentially deadly factor with which to contend.

While not for the faint of heart, this sequel will appeal to grown-ups who like a good scare. Despite the vaguely exploitative setup – this time out, the impromptu choice to go diving enables Roberts to have the main characters spend most of the movie in their underwear – the values that come to the fore as the ensemble struggles for survival are positive ones.

The film contains graphic, bloody shark attacks, gruesome images, a few obscene gestures and a couple of crass words. The Catholic News Service classification is A-III – adults. The Motion Picture Association of America rating is PG-13 – parents strongly cautioned. Some material may be inappropriate for children under 13.