Barsaat Ki Raat
It begins with the Roshan-Sahir Ludhianvi gem Garjat barsat sawan aayo re playing against the rain-drenched titles and setting the right romantic mood.
The reason for the title is provided later when the rains form a backdrop for the lead pair's first meeting. When hero Bharat Bhushan takes shelter from the rains in a canopied refuge, he finds a wet Madhubala there after her car breaks down. All the plot conventions we now know so well follow -- the heroine clutching at the hero when there is a flash of lightening, wringing water out of her clothes and fluttering nervously.
The meeting, of course, alters the course of their lives. Madhubala doesn't know that the man she met in the rains is the poet she so admires, until she hears him on the radio singing Zindagi bhar nahin bhulegi woh barsaat ki raat...