The German Doctor Florencia Bado, Àlex Brendemühl, Natalia Oreiro. Directed by Lucia Puenzo. Rated PG-13. Opens Friday.

The title character of The German Doctor is Josef Mengele, although Lucía Puenzo’s film plays unnecessarily coy about that for a little while. Set in Argentina in 1960, the movie finds the notorious Nazi scientist (Àlex Brendemühl) living under an assumed name as he hides from Nazi-hunters, and he first appears to young Lilith (Florencia Bado) and her family as a mild-mannered, helpful physician. But soon Mengele’s interest in Lilith’s small stature and her mother’s pregnancy turns unhealthy, and the movie becomes a (very) slow-burn thriller.

The gray visual palette matches the sedate tone of the film, which occasionally builds suspense but mostly unfolds too sleepily for any real excitement. In fictionalizing a true story, Puenzo (who adapted her own novel) allows herself the chance to explore the lives of new characters, but Lilith’s coming-of-age journey is as underdeveloped as Mengele’s potential for committing dangerous acts.