Closure (number 12)
Those who have read a Sherlock Holmes story will recognize that the conditions that set this plot twist in motion are fascinating. First and foremost, a pocket knife is given as a gift and appreciated. Second, someone commits a series of thefts in a short period of time. Third, a police officer meticulously records the information about the stolen pocket knife.
This is followed by an attempt to sell or otherwise demonstrate the pocket knife to an inappropriate person. When you sum it all up, you have a slew of crimes solved, all because someone donated a present that the receiver appreciated. That sounds like a Sherlock Holmes narrative, no doubt about it. I can even picture him mentally totaling everything up in his head. Who knew such things could happen in the real world?