The House On Telegraph Hill - Denouement
The final scenes take place inside the house, filmed on a Twentieth Century Fox soundstage.
Victoria discovers newspaper clippings revealing that her Aunt Sophie had died several days after she had received telegram notification from Alan of the death. She realizes he must have sent the telegram knowing he was about to kill her. Now she really is convinced he is after the inheritance and plans to kill her and her son Chris, too.
When Alan brings orange juices at bedtime she switches the glasses.
Alan realizes his plan to poison his wife has backfired. He rushes to the housekeeper Margaret for help and we learn they are lovers - she is in on the plan. But Margaret turns on him and refuses to call a doctor because he had wanted to include young Chris in his murder scheme. Never underestimate the maternal instinct.
And so justice is served as the poison does its job. The final frames show Victoria and Marc carrying the sleeping Chris away presumably to a new beginning for them all.