Casey wants nothing more than to be a detective. No mystery is too big or small for her to tackle! OK, so she doesn't see everything coming-mean girl Dina always has the last word, and Casey is constantly falling into embarrassing disasters in front of cute boy AJ. But now, it's Casey's eleventh birthday, and she's just been given a magnifying glass and a pair of binoculars-perfect gifts for today's mystery: Mr. Muffin, a cat Casey's parents insist is too big to be a hungry stray. Will Casey manage to convince them he belongs with her? More importantly, could that new girl in school be the perfect contender for a new best friend? Casey's on the job, and she won't stop till all cases are closed.