How should I end my story?

I was writing a story but now I am stuck at how to end it. Its about a pretty teenage girl was nicknamed as "the puppet" since she never really spoken in front of people, but is also extremely clever. The story is about how she and a boy she willing to speak to and obsessed about (which describe the big difference between people's impression toward her and her real characteristic), go through mystery cases that are unable to solve by the police.

Any ideas how should I end the story??
Thank you!!