I would say the tone of this sentence is formal.
Answer:
In many stories, the climax occurs at the point at which the major conflict in the story is resolved. ... In an adventure saga, the climax might take place when the characters reach their destination or find a treasure. In a tragedy, the death or fall of the hero or lead character may serve as the climax.
<em> hope this helped!</em>
The answer is the 4th one
it means that he couldn't find a sign of Nancy in the apartment