Final answer:
Without the context of the specific story or text, I cannot accurately determine who is at the door when Mr. White opens it. Doors in literature often symbolize pivotal moments or new character introductions.
Step-by-step explanation:
The question appears to be referencing the denouement of a story, where tension peaks as someone knocks or awaits entry at the door. Without specific context or a known story, I cannot confidently say who was at the door when Mr. White opens it. It's crucial to identify the text to give an accurate answer. However, the imagery of doors opening to reveal different characters or scenes is common in literature. Such a motif is often used to introduce pivotal moments or characters that propel the plot forward or culminate a story arc.