A change of pace for both director Vincente Minnelli and star Katharine Hepburn, this taut drama features the latter as Ann Hamilton, the daughter of a scientist (Edmund Gwenn), who after a whirlwind romance marries handsome but slightly mysterious inventor turned businessman Alan Garroway (Robert Taylor). But wedded bliss proves short-lived when Garroway refuses to discuss his brother Michael, whose presence is felt constantly despite the mystery surrounding his whereabouts. The missing Michael becomes an obsession for Ann, whose curiosity is piqued even more after a chance encounter with Sylvia Burton (Jayne Meadows), a young woman who figures in the lives of both brothers and who displays a strange resemblance to Ann herself. Despite Alan's dire misgivings, Ann feels compelled to solve the mystery of Michael, until, that is, she discovers that Alan may very well have murdered his own brother. Undercurrent marked the screen debut of Jayne Meadows and a breakthrough of sorts for Robert Mitchum, whom M-G-M borrowed from David O. Selznick for a reputed $25,000.
by Hans J. Wollstein synopsis