Name the observation
“The letter was returned” describes an event. “The recipient disappeared” offers an explanation. Keep the distinction in a reading notebook and notice when a character skips over it.
Offer an alternative
A name might be a label, an address might be old, and two people might share a description. An ordinary explanation can be as useful as an elaborate one. Ask what additional detail would distinguish them.
Return to the opening
Once the solution arrives, identify the detail that changed meaning and the information the author withheld. These stories are entertainment, not instructions for investigating real people or interfering with real cases.
Further reading
For source material and collection context, visit Library of Congress: collections. Check the collection’s own scope and access instructions before relying on it.