As with other Nazi war criminals, the notorious concentration-camp physician Josef Mengele — best known for selecting prisoners to die at Auschwitz and for his mad, unscientific “experiments” on victims — vanished to South America after World War II.

Mengele moved around the continent, always escaped capture and finally died there in 1979.

“The German Doctor,” an extraordinary, borderline-horror tale based in fact, is a reminder that all those years must contain actual stories.

Writer-director Lucía Puenzo has found a truly unnerving one in events surrounding Mengele’s 1960 association with a naive Argentine family, whose hotel on a pristine mountain lake becomes home to the fugitive for a while.

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The parties meet ominously: Mengele (Àlex Brendemühl), traveling alone under an alias, asks Enzo (Diego Peretti) if he can follow him and his family as they drive over a dangerous mountain road.

A longshot of Mengele’s car pulling too close to Enzo’s in a sudden storm says everything about what’s ahead once the monster insinuates himself into the lives of Enzo’s wife (Natalia Oreiro) and preteen daughter (Florencia Bado).

Puenzo masterfully balances the film’s thriller edge with disturbing details about Mengele’s obsession with genetic experimentation, as well as the community of German expatriates in Argentina helping old Nazis elude arrest.

Puenzo also tells us much through amazing visual associations: a visit to a doll-making factory, with shots of row upon row of perfectly similar, unfinished porcelain faces, is all we need to see to grasp Mengele’s unfinished dream of a “purified” master race.

Tom Keogh: tomwkeogh@yahoo.com