Things that seem like a bad idea: Getting into a mothballed Soviet sub, with a crew of angry Brits and boozy (and also angry) Russians, and secretly searching for lost Nazi gold at the bottom of the Black Sea. But Capt. Robinson (Jude Law) is undaunted, and so we have the predictably harrowing events of Kevin Macdonald's underwater thriller. And despite some stock characters and ludicrous science, Black Sea is a pretty decent, compact B-movie, by turns gritty, tense and nearly always entertaining. (It even has a splash of socio-economic commentary.) It breaks little ground in submarine drama — you can bring a checksheet of what will go wrong — but doubles down on mechanical problems by adding lots of money for the men to fight over as well.