Dil Hi To Hai (1963)

In a mansion, filled with guests and decorated for a wedding, two men struggle over the possession of a revolver. A shot rings out and to the horror of the assembled throng, a lady falls, dying. She is the mother of one of the protagonists and her deathbed confession is the key that unravels the complicated events that led up to this tragic climax - a tale that involves switched identities, multiple disguises, an arranged marriage, attempted murder, heartless cruelty, rapacious greed and (for good measure) a dancing girl whose mother (were she around) would have good reason to suspect her condition.