If you haven’t seen the movie, the basic plot until this point is:
Charming boy (Cary Grant) meets impossibly stylish girl (Deborah Kerr) on a cruise ship. They fall madly in love but both have fiancé’s waiting for them at home, so when the ship docks in New York they arrange to meet at the top of the empire state building in 6 months once they’ve sorted their lives out and can be together.
On her way to meet him, Deborah Kerr gets run over by a taxi and ends up unable to walk. She doesn’t want him to feel sorry for her so she doesn’t tell him, Cary Grant thinks that she stood him up and because she changed her mind.
We all think that might be it, until he spots her out somewhere and tracks her down at her apartment…